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MEDICAL 
ENTOMOLOGY 



Robert Matheson 

NEW YORK STATE COLLEGE OF AGRICULTURE 
CORNELL UNIVERSITY 



SECOND 
EDITION 



COMSTOCK PUBLISHING COMPANY, INC 

ITHACA, NEW YORK, 1950 



First Edition, 1932 
Copyright 1932 by Charles C Thomas 

Second Edition, 1950 

Copyright 1950 by 

Comstock Publishing Company, Inc. 



All rights reserved. This bool{, or any parts thereof, must 
not he reproduced in any form without permission 
in writing from the publisher, except by a reviewer who 
wishes to quote brief passages in a review of the boo\. 



PRINTED IN THE UNITED STATES OF AMERICA BY 
THE VAIL-BALLOU PRESS, INC., BINGHAMTON, N. Y. 



Preface 



MORE than seventeen years have passed since the first edition of Med- 
ical Entomology was published. In the original preface the important 
role played by insects and other arthropods in the transmission, causation, 
and spread of human and animal diseases was stressed. Today no such em- 
phasis is needed, for the important role of insects in human welfare was 
fully demonstrated during World War II. Recognition of the effects of 
insect-borne diseases on the armies and navies of the belligerents has impelled 
our medical and entomological services and the governments of all nations 
to conduct extensive investigations on all phases of the problem. The results 
of many of these investigations, some of which are continuing, have not yet 
been published. In the present work the writer has attempted, with varying 
-iiccess, to bring together all data available by the end of 1948. 

s completely rewritten text is offered to the physician, the entomologist, 
the public health worker, the student, and the layman in order to give them 
an authoritative survey of our present knowledge. The writer has not at- 
'empted to usurp the function of the physician, so the reader need not ex- 
pect to find a discussion of treatment; he will find, however, a brief account 
;>f the best known methods of controlling the insects involved in disease 
transmission or causation. Here great advances have been made during the 
^>ast few years. The reader is warned, however, that all the newer insecticides 
must be used with care and directions should be followed carefully. 

The literature on insect-borne diseases is voluminous, widely scattered in 
many and varied journals, monographs, government publications, and other 
sources, and difficult to cover adequately. For this reason a list of journals, 
textbooks, and other -publications that will enable the student to find the 
latest information is given at the end of the first chapter of the present work. 
Furthermore, each chapter is provided with a selected bibliography. Many 
of the references given have long bibliographies; these references are starred. 

The writer gratefully acknowledges his indebtedness to the numerous 



vi PREFACE 

authors whose publications he has consulted or quoted. Wherever illusl 
material is borrowed, full acknowledgment is given; if, by accident 
does not appear, due apology is hereby offered. To the many colle, 
friends, and students who have given suggestions, furnished material, a 
other ways co-operated with him, the writer desires to tender his s: 
thanks. He is under special obligation to Mr. Harvey I. Scudder for *- 
the galley proof, and to Mr. C. Y. Chow for checking the manuscn 
reference to malaria in China. 

ROBERT MATIIES 
Ithaca, New 
September 1949 




Plate IV. Left: Dr. Leland Ossian Howard (1857- ), who lor ncany thirty-five 
years served as Chief of the Bureau of Entomology, United States Department of Agri- 
culture, and who did more than any other American to establish the importance of in- 
sects as agents in the causation and spread of human disease. Right: Professor John Henry 
Comstock (1849-1931) in his old office in White Hall, Cornell University. By his work 
and teaching he gave entomology its present position in American universities. 



CHAPTER I 



Arthropods and Human Disease 



THE phylum Arthropoda plays a role in human welfare that is little under- 
stood by the great majority of people. In the sea the dominant animal life 
is not the larger fishes, mammals, etc., but those tiny animals that constitute 
the greater part of the plankton the free-swimming, minute Crustacea on 
which the others rely for food. As free-living vegetarians and scavengers they 
people the sea in vast numbers and perform their duties with admirable fitness, 
keeping great bodies of water cleaned of the dead and dying. On the land 
insects play a similar but more dominant role. For sheer vastness of numbers 
and incomparable adaptation for meeting the vicissitudes of life they far out- 
rank any other animal or plant association. (Who can count the ants that 
populate our fields and hillsides or the plant lice that suck their nourishment 
from our wild and cultivated plants?) The part insects play in agriculture and 
commerce has been admirably portrayed by a number of writers and, at times, 
overemphasized, especially with respect to the vast losses agriculture suffers 
at their hands. It is not our purpose to enter such a discussion here; the reader 
will find references at the end of this chapter that will enlighten him on 
this phase of insect activity. Sufficient for our purposes is the self-evident fact 
that, arthropods, and especially the class Hexapoda (insects), affect human 
welfare at every point and at times endanger man's very existence or hold 
in check his advances in the development of some of the most fertile regions 
of the globe. Medical entomology and parasitology have been recognized as 
important fields of study and research, not only for the zoologist, but for the 
physician, the veterinarian, and the layman. World War II amply dem- 
onstrated the great need for more knowledge of these subjects. 

No more striking and dramatic story could be told than that of the re- 
markable interrelations which arthropods play in the spread and maintenance 
of plant, animal, and human diseasefclnsects, long regarded and still regarded 
as unworthy of serious consideration 5^ many of our scientists, have gradually 
forced peoples and governments to devote some of their resources to studies 



2 MEDICAL ENTOMOLOGY 

too long delayed. Here only a bare outline of these studies can be offered and 
a tribute paid to those great medical leaders and others who have laid down 
their lives in the investigations of insect-borne diseases/) 

There are numerous early references to insects as distributors of disease 
references made long before the parasitic origin of disease was established. To 
Mercurialis (1530-1607), an Italian physician, is usually attributed the first 
concrete observation that flies serve, in some unknown manner, to spread 
disease. During the plague (Black Death), which ravaged Europe in his day, 
he observed that flies may spread the disease by feeding on the internal secre- 
tions of the dead and dying and then depositing their feces on the food of the 
well. Franca states that Souza (1587) suspected flies of spreading yaws (fram- 
boesia); Bancroft (1769) propounded a similar theory from his observations 
in Guiana; and many years later Castellani (1907) demonstrated that flies 
do play a part in the dissemination of this disease obtaining the organism 
(Treponema pertentie) from the sores of the sick and passing it on to the well. 

It was not till many years later that well-defined theories of insect propaga- 
tion of disease were promulgated. Such are those of Beauperthuy (1854) and 
Nott (1848) relative to the carriage of yellow fever by mosquitoes/Beau- 
perthuy thought that mosquitoes brought the disease from decomposing 
matter and injected it into man and this was long before the discovery of 
pathogenic bacteria by Pasteur in 1857. 

About the middle of the nineteenth century there was a remarkable develop- 
ment among German doctors and scientists in the study of helminths. Herbst 
in 1850 began the work of experimental parasitology when he fed trichinized 
meat to dogs and obtained the adult worms in his animals; Kiickenmeister 
in 1852 discovered, by feeding experiments, that the "bladder worms" in rabbits 
were but a stage in the life cycle of tapeworms; in 1854-1856 he also showed 
that "bladder worms" in pigs were but a stage in the life cycle of human tape- 
worms; Virchow and Leuckart in the same decade determined the life cycle 
of Trichinella (Trichina) and Leuckart (1862) solved the mystery of hydatid 
cysts. All these and other experimental activities undoubtedly fired the minds 
and guided the thinking of the rising generation^ 

s / 

DISEASES DISCOVERED TO BE TRANSMITTED BY INSECTS 

FILARIASIS: In 1863 Demarquay discovered a larval nematode in cases 
of chyluria; they were later seen by Wikherer in other cases, and Lewis (1872) 
discovered that the blood of man is the normal habitat of this filarial worm 
(Filaria sanguinis hominis of Lewis). 

In 1866 Dr. Patrick Manson, a young medical man of imagination and 



ARTHROPODS AND HUMAI^ DISEASE 3 

unbounded energy, left the shores of his native country, England, and took 
up heroic work first at Formosa and later (1871) at Amoy, China j(He in- 
vestigated anything and everything that came his way, developing a remarka- 
ble ingenuity for interpreting old and solving new problems^He found filaria 
abundant in the blood of his Chinese patients, established tfie "periodicity" of 
their appearance in the peripheral circulation, and in 1879 published the first 
account of an insect, Culex jatigans (the house mosquito of the tropics), 
serving as the intermediate host in the developmental cycle of a parasite. 
Though Manson traced the developmental cycle from the intestine through the 
tjhoracic muscles, he did not determine how the parasites reached a new host. 
He believed at that time that the life of the mosquito was short, the females 
dying after laying their eggs, and so he formulated the theory that man was 
infected by drinking the water in which infected mosquitoes died. It was not 
till 1900 that the true method was discovered by Low) Manson's work was 
the real starting point of medical entomology. In 1890 Manson returned to 
London, engaged in the practice of medicine, and urged the development 
of tropical medicine. In 1893 he evolved his mosquito theory of malaria. 
Though he never had an opportunity to test his theory, he so impressed his 
ideas on Dr. Ronald Ross that the latter eventually made his epoch-making 
discovery in 1897-1898. 

Only one other contribution by Manson can be recorded here. Loa loa, 
the African eye worm, was long identified both in America and Africa, but 
nothing was known of its life cycle. In 1891 Manson reported a new filaria 
in the blood of natives from the Congo and Old Malabar, naming it Filaria 
sanguinis hominis major (later known as Micro filaria diurna). On account 
of its diurnal periodicity Manson predicted that some bloodsucking, day- 
feeding fly would be found to be the intermediate host. From talks with the 
natives of Old Calabar he suggested that the "mangrove flies," Chrysops 
dimidiata and Chrysops spp., would prove the correct flies. In 1912 Leiper 
confirmed this prediction, and Kleine (1915) worked out the methods of 
transmission in detail. 

Another remarkable discovery should be recorded here; it, in fact, antedated 
Manson's work. Fedschenko (1869) demonstrated that Cyclops spp. (Crusta- 
cea) were the intermediate hosts of the famous "fiery serpent" of Moses, the 
dragon worm, Dracunculus medinensis Linn, (hence the name of the disease, 
dracontiasis). Manson (1894) confirmed and extended the work of Fed- 
schenko. 

MALARIA: In 1880 Laveran, working in Algeria, discovered the parasite 
of malaria in the red blood cells of his patients. More than ten years passed 



4 MEDICAL ENTOMOLOGY 

before Laveran's organism was accepted as the causal agent of the disease. 
Though much had been learned about the parasite during this time, little 
progress was made till Manson evolved his mosquito theory and impressed 
it on Ronald Ross, a young British surgeon working in India. So farfetched 
appeared Manson's theory that he was dubbed "Mosquito Manson" by his 
distinguished medical confreres and regarded as rather fit for a lunatic asylum. 
Curiously enough, in 1883 an American physician, A. F. A. King, had also 
propounded a mosquito malarial theory, which, unfortunately, fell on deaf 
ears and unimaginative minds. Under Manson's urging Ross continued to 
r work and in 1897 recorded his great discovery that "dappled-winged" mos- 
quitoes served as the definitive hosts of species of Plasm odium. Ross's work 
was done under the most trying conditions and at a time when no one knew 
mosquitoes or their biology. His results were fully confirmed by Bastianelli, 
Bignami, and Grassi (1898, 1899), Manson (1898), and Sambon and Low 
(1900). This discovery by Ross is undoubtedly one of the great landmarks 
in medical history, for it has led to the reduction, and can lead to the elimina- 
tion, of the most widespread and devastating of human diseases. 

PIROPLASMOSIS : While the mosquito malarial theory came to fruition 
in India and Europe, Theobald Smith, working in Washington, D.C., dis- 
covered the causative agent of Texas or red-water fever of cattle, Piroplasma 
bigemina, a red-blood-cell-inhabiting protozoan. In 1893 Smith and Kil- 
bourne published the results of their work. They demonstrated that the 
cattle tick, Boophilus annulatus Say. was the intermediate host. In addition, 
they showed thaTTKe^parasitc passes from the adult female ticks to their 
offspring and only young ticks (larvae) infect new hosts. This is the first 
instance of a protozoan passing by way of the egg to infect the young, which, 
in turn, transmit the disease to new hosts. Many other discoveries in the field 
of protozoan parasites of domestic animals have since been made and are of the 
greatest importance to animal husbandry. It would take us too far afield to 
discuss them here. 

TRYPANOSOMIASIS: From about 1893 to the present time the most 
remarkable discoveries have been made in the field of insect-borne diseases. 
These can be reviewed only briefly. In 1895 Bruce discovered Trypanosoma 
brucei, the causative agent of nagana or tsetse fly disease of cattle in Zululand 
and demonstrated that the tsetse fly, Glossina^mozsita&s Westw., could trans- 
mit the disease from the sick to the well. It was not, however, till 1909 that 
Kleine proved the developmental cycle in the fly and showed the true method 
of transmission. In 1901 Forde, in West Africa, observed a parasite in the 



ARTHROPODS AND HUMAN DISEASE 5 

blood of a European patient suffering from Gambian fever; later Dutton 
(1902) recognized it as a trypanosome and described it as Trypanosoma 
gambiense Dutton; Castellan! (1903) and Bruce and Nabarro (1903) proved 
this trypanosome was the causative agent of sleeping sickness and that Glossina 
palpalis R.-D. was the transmitting fly. In 1910 Stephens and Fantham de- 
scrfBed Trypanosoma rhodgsignsc as the etiological agent of Rhodcsian sleep- 
ing sickness, and Kinghorn and Yorke (1912) proved that Glossina morsitans 
Westw. was the transmitter. In South America Chagas (1909) demonstrated 
that a trypanosome, T. cruzi, was transmitted by a bug, Triatoma megista 
Burm. This parasite is the etiological agent of South American trypanosomiasis 
or what has been called Chagas' disease. 

YELLOW FEVER: While these African investigations were being devel- 
oped, the American Arrny Yellow Fever Commission, consisting of Reed, 
Carroll, Lazear, and Agramonte, made a still more remarkable discovery. 
They demonstrated (1900) that yellow fever can be transmitted only through 
the agency of the "tiger mosquito" or yellow-fever mosquito (Stegomyia 
jasciata, Aedes calopus, Aedes argenteus now known as Aedes jiegygti). 
Though Carlos Finlay, a Cuban physician, had as early as 1881 propounded 
a mosquito theory for yellow fever and had extensive experimental evidence 
in support of it, yet it must ever redound to the glory of this band of devoted 
workers that, because of their discoveries, one of the most deadly of human 
diseases could now be controlled or even eliminated. Though Noguchi (1919) 
announced that Leptospira icteroides was the etiological agent and his work 
was accepted by many workers, his results have since been abundantly dis- 
proved. It is now known to be caused by a recognized virus, which has been 
studied in great detail. For over a quarter of a century it was firmly be- 
lieved that the only transmitter of yellow fever was the "tiger mosquito" and 
that man was the only animal susceptible to the disease. On this belief 
prophylactic measures against yellow fever were based, and remarkable results 
were obtained in reducing and controlling outbreaks of the disease. However, 
in 1928 two most important contributions were made to the yellow-fever 
problem. Stokes and his associates, working in West Africa, demonstrated 
that monkeys, Macactts rhesus, were susceptible to the disease, and since then 
many more species of monkeys, both from the Old World and the New World, 
have been shown to be susceptible to yellow fever. In the same year Bauer, 
working in the same laboratory, proved that three other species of mosquitoes 
were capable of transmitting yellow fever. Since that date over thirty addi- 
tional species of mosquitoes have been shown to be capable oFtransmitting 
yellow fever. 



6 MEDICAL ENTOMOLOGY 

In 1933 Soper and his associates reported an outbreak, in parts o Brazil, 
of what has been designated as jungle yellow fever. Since then large areas in 
South America have been shown to be endemic centers of this disease. Jungle 
yellow fever is identical with classical yellow fever, but its epidemiology is 
remarkably different. (See pp. 353-356.) These and other discoveries have 
thrown new light on the yellow-fever problem. The development of an 
effective vaccine by the workers of the Rockefeller Foundation in 1932 has 
provided one of the most efficient methods to prevent and reduce yellow-fever 
outbreaks. 

^PLAGUE: In 1894 Yersin and Kitasato independently discovered the causa- 
tive agent of plague, Pasteurella pestis, and Yersin demonstrated that the dis- 
ease in man was identical with a plaguelike disease of rodents. Simond (1898) 
suggested that fleas _were agents in the dissemination of .plague, and his 
experiments showed that he was on the right track. In 1903-1904 Verjbitski 
demonstrated that fleas act as vectors of the plague bacillus, but his results 
were not published till 1908. The development of the plague bacillus in 
the gut of the rat flea was independently discovered by Listen (1905), and the 
role fleas play in the epidemiology of plague was fully determined by the 
British Plague Commission (1906-1908). Finally Bacot and Martin (1914) 
demonstrated the method of transmission of the plague bacilli by fleas. 

DENGUE: Dengue or breakbone fever, a disease of unknown etiology, 
was shown by Graham (1902) to be mosquito-borne, and his results were con- 
firmed by Ashburn and Craig (1907). Though the mosquitoes with which 
these investigators were supposed to have worked have since been shown 
not to be true vectors, their discovery was of great importance. The true vectors 
have since been shown to be Aedes aegypti and Aedes albopictus (see pp. 
357-358). 

PHLEBOTOMUS FLIES AND DISEASE: Pappataci fever (three-day 
fever or sand-fly fever), another disease of unknown etiology, was shown by 
Doerr, Franz, and Taussig (1909) to be transmitted by a sand fly, Phlebotomus 
papatasii (Psychodidae). Oroya fever, verruga peruana, or Carrion's disease, 
a disease of rather high mortality in parts of South America, was demon- 
strated by Townsend (1913-1914) to be transmitted by Phlebotomus verru- 
carum, and his results have been confirmed by Noguchi and his associates 
(1929). PhleJMomuS^h&ye. also been proved vectors of kala azar, Oriental 
sore, and espundia^(diseases known as -forms of leishmanjasis, the etiological 
agents being species ol~L^Tsfwania) , but at the present time (1949) many 
actual transmitters still remain unknown. 



ARTHROPODS AND HUMAN DISEASE 7 

SPIROCHETAL DISEASES: In 1903 a peculiar disease of fowls caused 
by Spirochaeta marchouxi Nuttall was shown by Marchoux and Salimbeni 
to be tick-borne, the common fowl tick, Argas persicus Oken, being the vector. 
Various recurrent fevers of man caused by Spirochaeta spp. have since been 
shown to be tick- or louse-borne. Ross and Milne (1904) first demonstrated 
that the tick, Ornithodorus moubata, is the vector of African relapsing fever 
caused by S. duttoni. These conclusions were confirmed and extended by 
Dutton and Todd (1905) working independently in the Belgian Congo. Since 
then various species of ticks (Argasidae) and lice (Pediculus humanus) have 
been shown to be the natural transmitters of the different relapsing fevers of 
man. Mackie (1907), working in India, first demonstrated the part played by 
lice (Pediculus corporis) in the dissemination of relapsing fevers. 

TSUTSUGAMUSHI DISEASE, KEDANI FEVER, FLOOD FEVER, 
OR JAPANESE RIVER FEVER: A serious disease in parts of Japan, China, 
Formosa, and other parts of the Far East, tsutsugamushi was first diagnosed 
as a distinct disease by Biilz and Kawakami in 1879. This peculiar disease had 
long been believed by the common people to be associated with the bites of a 
red mite. Balz and Kawakami concluded there was no such association. Kita- 
sato (1891-1893), however, decided that the bites of a red mite did play a role 
in the causation of the disease. The mite theory of the transmission of the 
disease has since been fully confirmed by the work of Tanaka (1899), 
Kitashima and Miyajima (1909, 1918), Miyajima and Okumura (1917), and 
others. The etiological agent was isolated by Nagayo and his associates (1930) 
and described as a rickettsia, R. orientalis. During World War II this disease 
was found to be widespread in many Eastern areas. The so-called "Mossman 
fever" of Australia, "scrub typhus" of Malaya and other parts of the East, 
and "pseuclotyphoid" of Sumatra were found to be kedani fever and trans- 
mitted by mites (Trombicula spp; see pp. 110-113). 

ROCKY MOUNTAIN SPOTTED FEVER: This peculiar disease prev- 
alent in Montana and certain other Rocky Mountain states was definitely 
proved by Ricketts (1906) to be transmitted to man by a tick, J^ermacentor 
under "soni Stiles (yenustus Banks). His results have been fully confirmed by 
various later workers, and Wolbach (1916, 1919) determined the causative 
agent to be Dermacentroxenu^ric^ettsi (Rickettsia bodies, so-called). This 
disease is now widespread in the United States (see pp. 73-74). 

TYPHUS FEVER: Though the head and body lice (Pediculus humanus 
var. capitis and var. corporis) have been closely associated with man in all his 
long career, it was not till 1909 that Nicolle, Comte, and Conseil, working in 



8 MEDICAL ENTOMOLOGY 

Tunis, demonstrated the role played by the body louse (corporis) in the 
spread of the much-dreaded typhus or jail fever. These results were confirmed 
by Ricketts and Wilder (1910) working independently in Mexico. Da Rocha- 
Lima (1916) discovered the causative agent and named it Ricl^ettsia prowa- 
zelji. During World War I (about 1915) a peculiar disease dubbed "trench 
fever" appeared among the troops of the contending armies and was definitely 
proved by various workers to be disseminated by head and body lice (see 
p. 208). Topfer (1916) designated what is considered the causal agent as 
Ricf^ettsia quintana. 

TULAREMIA: A peculiar plaguelike disease of rodents was investigated 
by McCoy (1911), and the etiological agent, Bacterium titlarense, was isolated 
and described by McCoy and Chapin (1912). In 1911 Pearse, in Utah, described 
a peculiar disease of man under the title of "insect bites," and this 
disease later became known as "deer-fly fever." Francis (1919-1920) recog- 
nized the identity of "deer-fly fever" of man and the plaguelike disease of 
rodents and named the disease tularemia. Francis and Mayne (1921) dem- 
onstrated that the deer fly, Chrysops discalis (Tabanidac), was the trans- 
mitting insect. Since then a large number of insects and ticks have been 
shown to be able to transmit the disease in nature. 

ONCHOCERCIASIS: Recent contributions in the field of medical en- 
tomology have been the solving of the life histories of Onchocerca volvulus 
Leuck. and O. caecutiens Brumpt (Nemathelminthes, family Filariidae). 
The former species occurs in Africa and the latter in parts of Central America 
and Mexico. Blacklock (1926) determined that 0. volvulus passes part of its 
life cycle in black flies (Eusimulium damnosum, family Simuliidae) while 
Hoffman (1930) and Strong (1931) demonstrated that O. caecutiens under- 
goes a developmental cycle in at least three species of black flies. Both these 
round worms produce diseased conditions in man. These two species are now 
considered to be one and the same, O. volvulus. 

In recent years several important diseases have been demonstrated to be 
insect-transmitted. Poliomyelitis, long associated with some bloodsucking 
insect as a vector, has been shown capable of being disseminated by filth- 
loving flies, as the housefly, blowflies, and flesh flies. How important a part 
these flies play has not been determined. St. Louis encephalitis, a new virus 
that appeared in epidemic form in St. Louis during 1933 and 1937 and has 
since been isolated in other parts of the country, has been shown to be dis- 
seminated to man by mosquitoes. The reservoir of this disease has been found 
in birds, primarily fowls, and in the fowl mite, Dcrmanyssus gallinae. Japa- 



ARTHROPODS AND HUMAN DISEASE 9 

nese B encephalitis, a serious disease in Japan and other parts of the East, 
has also been shown to be transmitted by mosquitoes. Equine encephalo- 
myelitis (several different strains), primarily a disease of horses, appeared also 
in man in Massachusetts in 1938 and in California in the same year. In 1941 
an extensive outbreak of human cases (over 3000) developed in the western 
prairie states of the United States and Canada. Mosquitoes have been proved 
to be the vectors of these diseases. 

OTHER ASPECTS OF DISEASE TRANSMISSION 

In the above survey nothing has been said of the mere mechanical carriage 
of pathogenic organisms by insects, especially filth-loving flies. Very early, 
flies, in the mind of the common people and the physicians, were associated 
with disease outbreaks. An abundance of flies during the summer presaged 
an unhealthy autumn, wrote Sydenham (r666), and since his time a long series 
of physicians and others have called attention to the abundance of and the 
dangers from filth-loving flies. Veeder (1898) called more specific attention 
to the housefly, and Reed, Vaughan, and Shakespeare (1900) outlined the 
role the housefly may play in the spread of typhoid fever. Since then the 
importance of filth-loving flies as possible disseminators of disease-producing 
organisms has been well established and recognized. 

This brief historical survey will indicate, to some extent, the role insects play 
in the dissemination of human diseases. Had the writer attempted to include 
animal diseases other than those of man, the list would have been much 
extended and the importance of insects, from the point of view of human 
welfare, more strikingly portrayed. In addition, the role insects play as vectors 
of plant diseases has become, during the past fifty years, almost as important 
as that in animal diseases. Rand and Pierce gave an extended account of the 
subject up to 1920, and since then the so-called "mosaics," "chloroses," and 
other "virus" diseases of plants and their transmission by insects have assumed 
even greater significance. 

In the gut of many insects are found representatives of the protozoan family 
Trypanosomidae, under the generic names Crithidia, Herpetomonas, Phyto- 
monas, Leishmania, Leptowonas, and others of doubtful validity. The rela- 
tionships of some of these forms to animal and plant diseases have been 
established, but the great majority of them remain undetermined. The prob- 
lem of isolating, ctilturing these forms, and of determining their relation to the 
insects, to other animals, and to plants is extremely difficult. Progress has been 



io MEDICAL ENTOMOLOGY 

made, and with the development of microtechnique we may expect much 
from the future. 



FACTORS INVOLVED IN DISEASE TRANSMISSION 

In the study of insect-borne disease, especially one in which the insect 
serves as the definitive or intermediate host, certain important considerations 
must always be kept in mind. Table i will serve to call attention to the more 
important features and indicate the far-reaching significance of the various 
factors involved. These factors are (i) the parasite or etiological agent; (2) the 
definitive host and the definitive reservoirs or nonreservoirs; (3) the method 
of transmission; (4) the intermediate host and the intermediate reservoirs or 
nonreservoirs; and (5) the method of transmission. The significance of these 
facts can be best illustrated by giving several examples. 

Table i. Three diseases and the factors involved in their transmission. 





Malaria 


Yellow fever 


Sleeping sickness 


Parasite (etiologi- 
cal agent) 


Plasmodittm vivax 
P. malariae 
P. jalciparum 


Virus 


Trypanosoma gambi- 
ense 


Definitive host 


Anopheles spp. 
How many? 


Aedes aegypti and 
many other spp. of 
mosquitoes. How 
many more? 


Glosslna palpal is 
Glossina spp. 
(How many?) 


Definitive host 
reservoirs 


? 


All not 
definitely known 


Game animals? 


Method of trans- 
mission 


Sporozoites 
Inoculative 


? 
Inoculative 


Infective salivary 
trypanosomes 
Inoculative 


Intermediate host 


Man 
Other animals? 


Man 
Monkeys 
Other animals? 


Man 
Domestic cattle? 


Intermediate host 
reservoirs 


Man with gameto- 
cytes in his blood 
Other animals ? 


Monkeys 
Other animals? 


Domestic cattle 
Game animals? 


Method of trans- 
mission 


Male and female 
gametocytes 
Ingested 


? 


Certain infective 
blood types of the 
trypanosome 
Ingested 



Examining such an outline, one is immediately struck by the lacunae, even 
in some of the best-known insect-borne diseases. In malaria it is apparent that 
the only definitive host reservoirs are mosquitoes (Anopheles spp.), but how 



ARTHROPODS AND HUMAN DISEASE 11 

long they can remain infected is still a matter of uncertainty. The number 
of Anopheles species that can act and the conditions under which they may 
serve as definitive hosts are still not well known, though much progress has 
been made toward solving these problems. In yellow fever the etiological 
agent (parasite) is a virus; only recently have the animal reservoirs been 
determined and, as yet, not all the mosquito transmitters have been recog- 
nized. Many factors in the problem of sleeping sickness remain unsolved. In 
a similar manner, data on all the insect-borne diseases could be assembled and 
the numerous unsolved problems pointed out. 

The literature dealing with medical entomology, parasitology, and preven- 
tive medicine has become of vast proportions, especially during the past fifty 
years. In each field, and we should include bacteriology and veterinary medi- 
cine, the entomologist will find texts, journals, reviews, summaries, etc., that 
he must consult if he is to keep abreast of the times. In addition to the refer- 
ences given at the end of each chapter, I am appending to this chapter a list 
of the more important journals, reviews, summaries, and other publications 
that the entomologist should consult. In many of the texts listed will be found 
bibliographies, some of them very extensive, and they should be of great benefit 
to those who desire to explore beyond the outer doorway. 

DEFINITION OF SOME OF THE TERMS EMPLOYED ABOVE 

Definitive Host. The host in which the sexual life of the parasite is passed. 
Intermediate Host. The host in which the asexual stages of the parasite are 

passed. 
Definitive Host Reservoir. Hosts in which a natural supply of the sexual stage 

of a parasite occurs. 
Intermediate Host Reservoir. Hosts in which a natural supply of the asexual 

stages of a parasite occurs. (In using these two terms the word host is fre- 
quently omitted.) 
Transmission. The passage of a parasite from the intermediate host to the 

definitive host or vice versa. 
Contaminative. Infection or transmission is said to be contaminative when 

the pathogenic organism gains entrance by way of abrasions, by fecal wastes 

deposited on the skin, etc. 
Inoculative. This term is applied when invasion of an organism takes place 

through the act of biting, the organism being inoculated during the feeding 

process. 
Ingestive. This applies when parasites are obtained at the time of feeding, the 

infective stage being ingested per os. 



12 MEDICAL ENTOMOLOGY 

REFERENCES 

Ashburn, P. M., and Craig, C. F. Experimental investigations regarding the 

etiology of dengue fever. Philip. Jl. Sci., B, 2: 93-147, 1907. 
Bacot, A., and Martin, C. J. Observations on the mechanism of the transmission 

of plague by fleas. Jl. Hyg., 13 (Plague Suppl. in): 423-439, 1914. 
Bancroft, E. An essay on the natural history of Guiana in South America. Lon- 
don, 1769. 
Bastianelli, G., Bignami, A. E., and Grassi, B. Coltivazione delle semilune mala- 

riche dell' uomo nell' Anopheles claviger Fabr.: nota preliminaire. Atti Re. 

Accad. Lincei, Rendic., 7 (ii): 313, 1898. 
Beauperthuy, L. D. Transmission of yellow fever and other diseases. Gaceta 

oficial de Cumana, Ano 4, No. 57, May 23, 1854. (Cited by Howard, Dyar, 

and Knab.) 

Boyce, R. Mosquito or man? The conquest of the tropical world. London, 1909. 
Bruce, D., and Nabarro, D. Progress report on sleeping sickness in Uganda. 

Repts. Sleep. Sick. Comm., Roy. Soc., No. i, 1903. 
Carter, H. R. Yellow fever, an epidcmiological and historical study of its place of 

origin. Baltimore, 1931. 

Castellani, A. Trypanosoma in sleeping sickness. Brit. Med. JL, i, p. 1218, 1903. 
Chagas, G. t)ber cine neue Trypanosomiasis des Mcnschens. Mem. do Instit. 

Oswaldo Cruz, i: 159-218, 1909. 

Dutton, J. E. Trypanosoma in man. Brit. Med. JL, T, p. 42; ii, p. 881, 1902. 
, and Todd, J. L. The nature of human tick fever in the eastern part of the 

Congo Free State, with notes on the distribution and bionomics of the tick. 

Liverpool School Trop. Med., Mem. xvm, 1905. 
Finlay, Carlos. Trabajos selectos. Selected papers. Havana, 1912. 
Finlay, Carlos E. Carlos Finlay and yellow fever. New York, 1940. 
Forde, R. M. Some clinical notes on a European patient in whose blood a 

trypanosome was found. JL Trop. Med. Hyg., 5: 261-263, 1902. 
Francis, E. Deer-fly fever; a disease of man of hitherto unknown etiology. U.S. 

Pub. Hlth. Repts., 34: 2061-2062, 1919. 
. The occurrence of tularaemia in nature, as a disease of man. Ibid., 36: 

*73 l -*7& I9 21 - 

, and Mayne, B. Experimental transmission of tularaemia by flies of the 

species Chrysops discalis. Ibid., pp. 1738-1746, 1921. 

Howard, L. O. A fifty year sketch history of medical entomology. Rept. Smith- 
sonian Inst. for 1921, pp. 565-586, 1928. 

Kelly, H. A. Walter Reed and yellow fever. New York, 1907. 

King, A. F. A. Insects and disease mosquitoes and malaria. Pop. Sci. Mon., 
23: 644-658, 1883. 



ARTHROPODS AND HUMAN DISEASE 13 

Kitashima, T., and Miyajima, R. M. Studien iiber die Tsutsugarnushikrankheit. 

Kitasato Arch. Exp. Med., 2: 91-146, 237-334, 1918. 
Listen, W. G. Plague, rats and fleas. Jl. Bombay Nat. Hist. Soc., 16: 253-274, 

1905. 

Mackie, F. P. The part played by Pediculus corporis in the transmission of re- 
lapsing fever. Brit. Med. JL, 2, p. 1706, 1907. 
Manson, P. The filaria sanguinis hominis and certain new forms of parasitic 

disease in India, China, and warm countries. London, 1883. 
. Surgeon-Major Ronald Ross's recent investigations on mosquito malaria 

theory. Brit. Med. JL, i, pp. 1575-1577, 1898. 
Manson-Bahr, P. H., and Alcock, A. The life and work of Sir Patrick Manson. 

London, 1927. 
Marchoux, E., and Salimbeni, A. La spirilose des poules. Ann. Inst. Pasteur, 

17: 569-580, 1903. 
Miyajima, M., and Okumura, T. On the life-cycle of the "Akamushi." Kitasato 

Arch. Exp. Med,, i: 1-14, 1917. 
Nicolle, C. Reproduction experimentale du typhus exanthematique chez le singe. 

C. R. Acad. Sci., Paris, 149: 157-160, 1909, 

, Comte, C., and Conseil, E. Transmission experimentale du typhus exanthe- 
matique par le pou du corps. Ibid., pp. 486-489, 1909. 
Nott, J. C. On the origin of yellow fever. New Orleans Med. and Surg. JL, 

4: 563-601, 1848. 
Nuttall, G. H. F. On the role of insects, arachnids, and myriapods as carriers in 

the spread of bacterial and parasitic diseases of man and animals. Johns Hopkins 

Hosp. Rcpts., 8, 1899. 

Rand, F. V., and Pierce, W. D. A co-ordination of our knowledge of insect trans- 
mission in plant and animal diseases. Phytopathology, 10: 189-231, 1920. 
Reed, Walter. The etiology of yellow fever. Phila. Med. JL, 6: 790-796, 1900. 
Rickctts, H. T. The transmission of Rocky Mountain spotted fever by the bite 

of the wood tick (Dermacentor occidcntalis). JL Amer. Med. Assoc., 47: 358, 

1906. 
, and Wilder, R. M. The transmission of typhus fever of Mexico (tarbar ditto) 

by means of the louse (Pediculus vestimenti). Ibid., 54: 1304-1307, 1910. 
Rocha-Lima, H. da. Zur Aetiologie des Fleckfiebers. Berlin. Klin. Woch., 53 (i) : 

567, 1916. 
. Untersuchungen iiber Fleckfieber. Munch. Med. Woch., 63 (No. 39): 

1381-1384, 1916. 

Ross, Ronald. Pigmented cells in mosquitoes. Brit. Med. JL, i, pp. 550-551, 1898. 
Ross, R. H., and Milne, A. D. Tick fever. Ibid., 2, pp. 1453-1454, 1904. 
Sambon, L. W., and Low, G. The malaria experiments in the Campagna. Ibid., 

2, pp. 1679-1682, 1900. 



i 4 MEDICAL ENTOMOLOGY 

Simond, P. La propagation de la pcste. Ann. Inst. Pasteur, 12: 625-687, 1898. 

Smith, T., and Kilborne, F. L. Investigations into the nature, causation and pre- 
vention of Texas or southern cattle fever. U.S. Dept. Agr., Bur. Animal Ind., 
Bull, i, 1893. 

Tanaka, K. Uber Aetiologie und Pathogenese der Kedanikrankheit. Central. 
Bakt, I Abt. 26: 432-439, 1899. 

Veeder, M. A. Flies as spreaders of sickness in camps. Medical Rec., 54: 429- 
430, 1898. 

Verjbitski, D. T. The part played by insects in the epidemiology of plague. Jl. 
Hyg., 8: 162-208, 1908. 

Wolbach, S. B. The etiology of Rocky Mountain spotted fever. Jl. Med. Res., 
34: 121-126, 1916. 

. Studies on Rocky Mountain spotted fever. Ibid., 41: 1-197, 1919. 

SOME OF THE MORE IMPORTANT JOURNALS 

American Journal of Hygiene. Baltimore, 1921-. 
American Journal of Public Health. New York, 1911-. 
American Journal of Tropical Medicine. Baltimore, 1921-. 
Annales de 1'Institut Pasteur. Paris, 1887-. 
Annales de parasitologie humaine et comparce. Paris, 1923-. 
Annals of Tropical Medicine and Parasitology. Liverpool, 1907-. 
Archiv fur SchifTs- und Tropen-Hygiene. Leipsic, 1897-. 
Archives de 1'Institut Pasteur. Tunis, 1906-. 
Archives de parasitologie. Paris, 1898-1919. 
Brasil-Medico. Rio de Janeiro, 1887-. 
British Medical Journal. London, 1857-. 
Bulletin biologique de la France et de la Belgique. 1869-. 
Bulletin of Entomological Research. London, 1910-. 
Bulletin de 1'Institut Pasteur. Paris, 1903-. 
Bulletin de la societe de pathologic exotique. Paris, 1908-. 
Ceylon Journal of Science, Section D, Medical Science. Colombo, 1924-. 
Index Medicus. Washington, D.C., 1879-. 
Indian Journal of Malariology. Calcutta, 1947-. 
Indian Medical Gazette. Calcutta, 1866-. 
Indian Medical Research Memoirs. Calcutta, 1924-. 

International Health Board, Annual Reports and Publications. New York, 1913-. 
Journal of the American Medical Association. Chicago, 1883-. (Contains refer- 
ences to most of the current medical literature.) 
Journal of Economic Biology. London, 1906-. 
Journal of Economic Entomology. Geneva, N.Y., 1908-. 
Journal of Hygiene. Cambridge, England, 1901-. 



ARTHROPODS AND HUMAN DISEASE 15 

Journal of the London School of Hygiene and Tropical Medicine. London, 1911- 

I 9 I 3- 
Journal National Malaria Society. Pub. Nat. Malaria Soc., 1942-. 

Journal of Parasitology. Urbana, 111., 1914-. 
Journal of the Royal Army Medical Corps. London, 1903-. 
Journal of Tropical Medicine and Hygiene. London, 1898-. 
Kitasato Archives of Experimental Medicine. Tokyo, 1917-. 
Liverpool School of Tropical Medicine, Memoirs. Liverpool. 
Malariologia. Rome, 1908-. 

Medical Department, United Fruit Company, Annual Reports. New York, 1912-. 
Memorias do Institute Oswaldo Cruz. Rio de Janeiro, 1909-. 
Parasitology. Cambridge, England, 1908-. 
Philippine Journal of Science, Series B. Manila, 1906-. 
Redia. Florence, Italy, 1903-. 

Reports of the Wellcome Research Laboratory. Khartum, 1906-. 
Review of Applied Entomology, Series B (Medical and Veterinary). London, 
1913-. (Contains reviews of practically all literature in the field of medical 
and veterinary entomology; each volume is thoroughly indexed by author and 
subject.) 

Rev. Inst. Salubr. y Enferm. Trop. Mexico, D.F., 1939-. 
Royal Society of London, Proceedings, Series B. London, 1905-. 
Scientific Memoirs by Officers of the Medical and Sanitary Department of the 

Government of India. Calcutta. 
Sleeping Sickness Bureau Bulletin. London, 1908-1912. (Continued as Tropical 

Diseases Bulletin.) 

Sleeping Sickness Commission of the Royal Society, Reports. London, 1903-. 
Transactions of the Congresses of the Far Eastern Association of Tropical Medi- 
cine. 1911-. 
Transactions of the Royal Society of Tropical Medicine and Hygiene. London, 

1907-. 
Tropical Diseases Bulletin. London, 1912-. (The most valuable publications for 

it contains critical reviews of all literature within its field; well indexed.) 
Tropical Veterinary Bulletin. London, 1912-. 

United States Department of Agriculture. Bulletins, Reports, Circulars, etc. 
Washington, D.C. 

Bureau of Animal Industry, Bulletins, Reports, Circulars, etc. 
Bureau of Entomology, Bulletins, Reports, Circulars, etc. 

United States Public Health Service, Weekly Reports, Bulletins, publications of 
various kinds. Washington, D.C. 
Hygienic Laboratory, 1 Bulletins, etc. 

1 Now known as the National Institute of Health. 



16 MEDICAL ENTOMOLOGY 

BOOKS OF IMPORTANCE TO THE MEDICAL 
ENTOMOLOGIST 

Alcock, A. Entomology for medical officers. 2nd ed. London, 1920. 

Belding, D. L. Textbook of clinical parasitology. New York and London, 1942. 

Brumpt, E. Precis de parasitologie. 4th ed. Paris, 1927. 

, and Neveu-Lemaire, M. Travaux pratique de parasitologie. Paris, 1929. 

Byam, W., and Archibald, R. G. (editors). The practice of medicine in the tropics. 
London, 1921-1923. 3 vols. 

Carpenter, G. D. H. A naturalist on Lake Victoria. London, 1920. 

Castellani, A., and Chalmers, A. J. Manual of tropical medicine. 3rd ed. Lon- 
don, 1919. 

Chandler, A. C. Introduction to human parasitology. 8th ed. New York, 1949. 

Comstock, J. H. An introduction to entomology. 9th ed. Ithaca, N.Y., 1947. 

Craig, C. F. A manual of the parasitic protozoa of man. Philadelphia, 1926. 

, and Faust, E. C. Clinical parasitology. Philadelphia, 1943. 

Culbertson, J. T. Immunity against animal parasites. New York, 1941. 

Doane, R. W. Insects and disease. New York, IQIO. 

Ehlers, V. M., and Steel, E. W. Municipal and rural sanitation. New York, 1927. 

Ewing, H. E. A manual of external parasites. Springfield, 111., 1929. 

Fantham, H. B., Stephens, J. W. W., and Theobald, F. V. The animal parasites of 
man. London and New York, 1916. 

Faust, E. C. Human helminthology. 2nd ed. Philadelphia, 1939. 

Folsom, J. W. Entomology, with special reference to its biological and economic 
aspects. 3rd ed. Philadelphia, 1922. 

Fox, C. Insects and disease of man. Philadelphia, 1925. 

Hall, M. C. Arthropods as intermediate hosts of helminths. Smithsonian Misc. 
Coll., 81, No. 15, 1929. 

Hegner, R. W., Root, F. M., and Augustine, D. L. Animal parasitology. New 
York, 1928. 

, Root, F. M., Augustine, D. L., and HufT, C. G. Parasitology with special 

reference to man and domesticated animals. New York, 1938. 

Henneguy, L. F. Les insectes. Paris, 1904. 

Herms, W. B. Medical and veterinary entomology. 3rd ed. New York, 1939. 

Herrick, G. W. Insects injurious to the household and annoying to man. New 
York, 1926. 

Howard, L. O. A history of applied entomology. Smithsonian Misc. Coll., Vol. 
84, 1930. 

. The insect menace. New York, 1931. 

Hull, T. G., et al. Diseases transmitted from animals to man. 3rd ed. Spring- 
field, 111., 1947. 

Imms, A. D. A general textbook of entomology. 3rd ed. London, 1934. 



ARTHROPODS AND HUMAN DISEASE 17 

International Congress of Tropical Medicine and Malaria. Proceedings of the 

fourth International Congress, 1948. Washington, D.C., 1949. 2 vols. 
Laloy, L. Parasitisme et mutalisme dans la nature. Paris, 1926. 
Mackie, T. T., Hunter, G. W., and Worth, C. B. A manual of tropical medicine. 

Philadelphia, 1945. 

Manson-Bahr, P. H. Manson's tropical diseases, nth ed. London, 1940. 
Martini, E. Lehrbuch de medizinschen Entomologie. Jena, 1923. 
Mense, C. (editor). Handbuch de Tropen-Krankheiten. 3rd ed. 1924-1929. 5 

vols. 

Napier, L. E. The principles and practice of tropical medicine. New York, 1946. 
Neveu-Lemaire, M. Traite d'helminthologie medicale et vcterinaire. Paris, 1936. 
Patton, W. S., and Cragg, F. W. A textbook of medical entomology. Calcutta 

and London, 1913. 
, and Evans, A. M. Insects, ticks, mites, and venomous animals of medical 

and veterinary importance. Part i, Medical; Part H, Public health. Croydon, 

England, 1929-1931. 

Riley, W. A., and Johannsen, O. A. Medical entomology. New York, 1932. 
Rosenau, M. J. Preventive medicine and hygiene. 5th ed. New York, 1927. 
Ross, Sir Ronald. The prevention of malaria. London, 1910. 
Roy, D. N. Entomology (medical and veterinary). Calcutta, 1946. 
Russell, P. M., West, L. S., and Manwcll, R. D. Practical malariology. Philadel- 
phia, 1946. 

Scott, H. H. A history of tropical medicine. London, 1939. 2 vols. 
Smart, John. A handbook for the identification of insects of medical importance. 

British Museum, London, 1943. 2nd ed., 1948. 
Stiles, C. W., and Hassall, A. Key-catalogue of the Crustacea and arachnoids of 

importance in public health. U.S. Pub. Hlth. Serv., Hyg. Lab. Bull. 148, 1927. 
Strong, R. P. Stitt's diagnosis, prevention and treatment of tropical diseases. 

Philadelphia, 1943. 2 vols. 
Symposia (all by many authors): 

A symposium on human malaria. (Amer. Assoc. Adv. Sci., Pub. 15.) Wash- 
ton, D.C., 1941. 

A symposium on relapsing fever in the Americas. (Ibid., Pub. 18.) Washing- 
ton, D.C., 1942. 

Virus and rickettsial diseases. Cambridge, Mass., 1940. 

Taliaferro, W. H. The immunology of parasitic infections. New York, 1929. 
van Zwaluwenburg, R. H. The interrelationships of insects and roundworms. 

Hawaii Sugar Planters Assoc., Bull. Exp. Sta., No. 20 (Ent. ser.), 1928. 
Wardle, R. A. The problems of applied entomology. New York, 1929. 
Watson, M. Rural sanitation in the tropics. New York, 1915. 
Wenyon, C. M. Protozoology. London, 1926. 2 vols. 



CHAPTER II 



The Arthropoda 



THE Arthropoda constitute the largest of the animal phyla. They are 
bilaterally symmetrical animals. The body is divided into rings or seg- 
ments of which several or many bear jointed appendages. They possess an 
exoskeleton composed mainly of chitin. During growth the external skeleton 
is periodically molted in its entirety. The nervous system consists of a pair of 
ganglia to each segment, the ganglia being connected longitudinally and lat- 
erally by commissures. It is located below the gut and forms a collar about it 
in the head where the brain is located. The blood circulatory system consists 
of a longitudinal dorsal vessel or heart. It is perforated and contractile, the 
pulsations usually proceeding from the posterior to the anterior end. There 
is no closed system of blood vessels, the blood flowing freely about the internal 
organs. 

CLASSIFICATION OF THE ARTHROPODA 

The phylum is divided into a rather large number (about thirteen) of classes. 
Only five of these are of interest to the student of medical entomology. Four 
of the five classes will be dealt with in some detail in the following chapters. 
In order not to burden the text with too much morphological detail the main 
structures of each class will be given under the discussion of the group. The 
following key will aid in separating the main classes of the Arthropoda : 

1. With two pairs of antennae and usually at least five pairs of ambulatory 

legs; respiration by means of blood gills; all aquatic or semi- 
aquatic Crustacea 

2. Without antennae; with only four pairs of ambulatory legs; respiration 

aerial by means of trachea or the surface of the body. (Scorpions, 
spiders, mites, etc.) Arachnida 

3. With only one pair of antennae; respiration aerial 4 

4. With only three pairs of legs and usually with wings in the adult state. 



THE ARTHROPODA 19 

(Insects) Hexapoda 

With more than three pairs of legs; wings absent 5 

5. With two pairs of legs on many of the body segments. (Millepedes). 

Diplopoda 

With one pair of legs on each of the body segments. (Centipedes). 
Chilopoda 

THE CLASS CRUSTACEA 

The Crustacea constitute a large class of almost exclusively aquatic animals. 
They occupy ponds, lakes, and streams and are the dominant form of animal 
life in the sea. Some species, such as sow bugs and pill bugs, are terrestrial and 
are generally found in damp situations. The more common representatives are 
the crayfishes, lobsters, shrimps, water fleas, etc. In the waters of the world they 
play a part closely parallel to that which insects play on the land. The great 
majority are free-living, feeding on aquatic plants, preying on animals, and 
performing the important function of scavengers of the waters. Like insects, 
many species are represented by enormous numbers of individuals, and the 
waters teem with their countless millions. The minute Crustacea furnish the 
main food for the larger aquatic animals. Despite their numbers and abun- 
dance, comparatively few species are known to play a part in the transmission 
of human parasites. 

BRIEF SYNOPSIS OF THE CRUSTACEA 

The class Crustacea is divided into two subclasses, the Entomostraca and 
the Malacostraca. Both of these subclasses contain a few species that serve as 
intermediate hosts of human parasites. 

THE SUBCLASS ENTOMOSTRACA: This subclass contains an im- 
mense number of small marine and fresh-water forms. Most of them are 
free-living, though some lead a parasitic life. They are of great importance 
since they constitute the main food supply of the larger aquatic animals, espe- 
cially the fishes. This subclass is divided into four orders Phyllopoda, Ostra- 
coda, Copepoda, and Cladocera. Although representatives of all these orders 
serve as intermediate hosts of animal parasites, only the members of the Cope- 
poda have been so far involved in human infections. 

THE SUBCLASS MALACOSTRACA: This group contains the larger 
Crustacea such as the lobsters, crayfishes, and crabs. It is divided into a number 
of orders, of which only the Decapoda are known to act as intermediate hosts 
of human parasites. 



20 MEDICAL ENTOMOLOGY 

CRUSTACEA AND HUMAN DISEASE 

A few of the Crustacea bear an important relation to human diseases. Cer- 
tain of them act as secondary or intermediate hosts of human parasites. 
Dracunculus medinensis, the Guinea worm, passes its larval stage in various 
species of copepods 1 belonging to the genus Cyclops (Fig. i). Man and other 
animals become infected by drinking raw water containing parasitized 
Cyclops spp. This disease has been known from antiquity, and Moses referred 
to it as "the fiery serpent." When infected Cyclops spp. are swallowed, the 
larvae of Dracunculus medinensis escape and penetrate the wall of the stomach 
or intestine. They migrate through the tissues, lodging at last in the sub- 
cutaneous connective tissue. It requires from 10 to 14 months for the females 
to reach maturity. The females measure from 70 to no cm. in length. When 
mature the females produce blisterlike lesions on the lower extremities as the 
feet and ankles (Fig. 2) and also on other parts of the body. The breaking 
of these lesions enables the parasites to discharge their young small Hlarial 
worms. These are discharged whenever the infected member comes in contact 
with fresh water. Dogs, horses, cattle, and other animals serve also as hosts 
of this parasite and undoubtedly aid greatly in its spread and prevalence in 
any region where it has become established. Owing to the fact that no clinical 
symptoms appear until the females arc mature and that there is no known 
method of early diagnosis, persons harboring this parasite may unknowingly 
spread it from one region to another. 

The presence of this worm causes no symptoms of disease until the forma- 
tion of the lesions. Then occurs intense itching followed by nausea, vomiting, 
diarrhea, severe dyspnea, and giddiness. These conditions are supposed to be 
due to the toxic secretions of the worm. 

The Guinea worm is widely distributed. It occurs over vast areas in Africa, 
Iran, India, southern Russia, the islands of the Caribbean Sea, the Guianas, and 
parts of Brazil. It is also found in North America in fur-bearing animals such 
as foxes, raccoons, minks, and dogs. There is no effective treatment except the 
removal of the worms. Prophylaxis consists in drinking only boiled or filtered 
water and in preventing infected persons from coming in contact with water 
used for drinking purposes. 

Another important human parasite, Diphyllobothrium latum, the broad fish 
tapeworm, has become well established in certain sections of North America. 
The early larval stages of this parasite develop in certain fresh-water Crustacea 

1 These are frequently called "water fleas," a term that is restricted to the cladocerans 
(Daphnia and its allies). 



THE ARTHROPODA 21 

of the genera Cyclops and Diaptomus. These infected crustaceans are eaten 
by plankton-feeding fishes such as pike, pickerel, and turbot. Within the fish 
the parasitic larvae escape and penetrate through the wall of the stomach. In 
the course of a few days these larvae imbed themselves in the fleshy tissues, 
where they remain in a sort of encysted condition (plerocercoids) . Man be- 
comes infected by eating partially cooked or raw fish. The tapeworm becomes 
mature in from five to six weeks after the ingestion of the larva by man. 




Fig. i (left). Cyclops sp., with eggs attached. 

Fig. 2 (center). Guinea worm partially extracted from the fourth toe. (From Castellani 
and Chalmers, Manual of Tropical Medicine.) 

Fig. 3 (right). Chelicera of a spider, somewhat diagrammatic. D, duct from poison 
gland; F, fang; O, opening of poison gland; P, poison gland. 

This parasite is widely distributed in Europe, parts of Africa, and in Siberia, 
Japan, and Manchuria; it is well established in central North America. The 
plerocercoids have been found in fishes from most of the large lakes of the 
Canadian prairies, from lakes in northern Minnesota and northern Michigan, 
and from the Greak Lakes as far east as Lake Erie. As cats, dogs, foxes, bears, 
and probably other fish-eating animals, as well as man, are hosts of the adult 
tapeworm, the widespread distribution of this parasite is assured. 

In man the tapeworm causes a rather serious disease. The clinical symptoms 
are those of severe anemia, reduced hemoglobin and general weakness. 
Prophylaxis consists in the thorough cooking of all fish intended for food. 

The lung fluke, Paragonimus wester mani, passes part of its larval life in 
fresh-water crayfishes and crabs. The adults are found in the lungs of man, 
cats, dogs, foxes, wolves, pigs, and many other animals. It occurs principally 
in the Far East (Japan, Korea, Formosa, French Indo-China, Siam, Federated 



22 MEDICAL ENTOMOLOGY 

Malay States, Bengal, Assam, Madras, and the Philippines) and is recorded 
from parts of Africa, the Dutch East Indies and in certain areas of South and 
Central America. The life cycle of the fluke is rather complicated, involving a 
snail (a species of the genus Melania) and then a fresh-water crayfish or 
crab. Man becomes infected by eating the raw flesh of these animals. The 
nature of the diseased condition produced by this worm in man depends on 
the localization of the parasite. Though normally a parasite of the lungs, it 
may invade various organs, even the brain. As no effective treatment appears 
to be known, it would seem imperative that only thoroughly cooked meat of 
fresh-water crayfishes and crabs should be eaten. 

Table 2. Interrelation of Crustacea and human parasites. 



Parasite 


Organ attacked 


Primary 
hosts 


Intermediate hosts 


First 


Second 


Dracunculus 


Migrates through 


Man, cats, 


Cyclops 


None required 


medinensis 


subcutaneous 


monkeys, 


bicuspidatus 




(Guinea worm) 


tissues 


dogs, foxes, 


C. corona t us 








etc. 






Diphyllobothrium 


Intestine 


Man, cats, 


Cyclops 


Esox Indus 


la turn 




dogs, foxes, 


strenuus 


Stizostcdion 


(broad fish 




bears, pigs, 


Diaptomus 


I'ltreum 


tapeworm) 




mink, 


oregonensis 


S. canadcnsc 






etc. 


D. vulgar is 


S. griscum 








D. gracilis 


l^ota maculosa 








D. graciliodes 


Pcrca flavesccns 










and many others 


Paragonimus 


Lungs and 


Man, cats, 


Melania 


Astacus japonicus 


wcstermant 


occasionally 


dogs, wolves, 


liber tin a 


A. si mil is 


(lung fluke) 


other organs 


pigs, beavers, 


Melania spp. 


Potamon dchaani 






tigers, etc. 


(snails) 


P. obtusipes 










and others 



THE CLASS ARACHNIDA 

Scorpions, Pseudoscorpions, Spiders, Mites, Ticks 

The Arachnida are air-breathing arthropods. The body is usually divided 
into two regions the cephalothorax, including the fused head and thorax, 
and the abdomen. The abdomen may be either segmented or unsegmented. 
In the mites and ticks the entire body is fused and forms a kind of sac. The 
head appendages are highly modified. The antennae are lacking and the eyes, 
when present, are rather simple and sessile. In the adults there are four pairs 
of ambulatory legs and these are attached to the cephalothorax. The first stage 
or larva has only three pairs of legs. The organs of respiration, when present, 



THE ARTHROPODA 23 

consist of either tracheae or book lungs. The sexes are distinct and the meta- 
morphosis is incomplete, the young closely resembling the adult. 

The arachnids suck the juices 2 of their victims by means of a sucking 
stomach. The mouth parts are adapted either for crushing their prey and 
sucking up the liquid portions or for piercing and cutting the tissues of their 
hosts (parasitic forms) in order to obtain blood. The mouth parts consist of 
a pair of cheliccrae 3 located in front of the mouth opening; a pair of pcdipalpi, 
the palpi or palps, situated either at the sides of the mouth or immediately be- 
hind it; and, in many forms, a peculiar structure known as the hypostome. 
The hypostome is most highly developed in some of the parasitic forms and 
is fully discussed later. It is located, when present, directly beneath the mouth 
opening. The structure of the cheliccrae varies greatly in the different orders 
of the Arachnida. In the spiders (Araneida) each chelicera consists of a large 
basal segment and a terminal clawlike one (Fig. 3). By means of these 
appendages the spider seizes and kills its prey. Near the tip of the claw is 
the opening of the poison gland. In the parasitic forms (ticks, etc.) the cheli- 
cerae are modified to serve as cutting and piercing organs. They are fully dis- 
cussed and illustrated in the following chapter. The pedipalpi are more or 
less leglike in all the groups and consist of four to six segments. In the spiders 
the pcdipalpi 4 of the male are greatly modified into very specialized organs 
for the transference of the semen to the females. In many of the ticks they 
serve as organs for the protection of the highly developed piercing organs. 

SYNOPSIS OF THE ARACHNIDA 

The class Arachnida is divided into nine to twelve orders. From the stand- 
point of the medical workers, only six of these orders are known to be of im- 
portance. Of these six, only one, the Acarina, is of sufficient importance to be 
treated in any detail. The other five contain forms which possess poison glands. 
Their bites or stings, when they do attack humans, may be of such severity as 
to require medical attention. Certain of these forms are treated in a brief 
chapter (Chapter xix) dealing with the poisons of arthropods. 

The following key will aid in separating the more common orders of 
Arachnida. 



2 The solpugids and the harvestmen (daddy longlegs) are supposed to take solid food. 

3 The chelicerae are homologous to the second antennae of the Crustacea and have 
become modified into prehensile or cutting organs; the true antennae, the first antennae 
of Crustacea, are lost in the spiders. In insects the true antennae are retained but the 
second antennae are lost. 

4 For an extended account see Comstock, The Spider Boo\ (1948). 



24 MEDICAL ENTOMOLOGY 

1. Abdomen distinctly segmented 2 

Abdomen not distinctly segmented 4 

2. Abdomen armed with a taillike prolongation. (Scorpions) .... Scorpionida 
Abdomen without a taillike prolongation 3 

3. Palpi chelate or with pincerlike claws. (Pseudoscorpions) 

Pseudoscorpionida 

Palpi not chelate or without pincerlike claws Pedipalpida 

Solpugida 

4. Abdomen joined to the cephalothorax by a short, narrow stalk. (Spi- 

ders) Araneida 

Abdomen fused with the cephalothorax, forming a saclike body . . Acarina 

THE ORDER ACARINA 

The Acarina are rather small to minute arachnids. The largest, such as 
some fully gorged ticks, may reach a length of nearly 25 mm., while the small- 
est rarely exceed 0.25 mm. in length. The order contains a large number of 
species. Like the insects and crustaceans, the species arc noteworthy for the 
vast number of individuals. The body is depressed dorsoventrally and is un- 
doubtedly an adaptation for their mode of life. The head, thorax, and ab- 
domen are fused, giving them a saclike appearance. In some cases the cephalo- 
thorax may be demarcated from the abdomen by a groove or furrow. The body 
may be partially or completely covered by a scutum or shield. The mouth parts 
are located either anteriorly or on the anterior ventral surface. These structures 
are described in detail in the discussion of the various orders of mites. Eyes are 
either present or absent; when present they consist of simple convex facets 
and are generally located on the margin of the scutum or on folds on the 
ventral surface. The respiratory organs, when present, consist of tracheae 
connected to the exterior by means of spiracles. The spiracles are usually 
located on chitinized plates and may be either in pairs or singly. Some groups, 
as the sarcoptic and demodectic mites, lack tracheae, the animals breathing 
directly through their body wall. The sexes are distinct, the males generally 
smaller than the females. The opening of the reproductive organs is located 
on the ventral surface, usually directly behind the mouth parts. The digestive 
system consists of a straight tube, often supplied with numerous tubular 
branches. The anal opening is either ventral or dorsal, rarely terminal. 

The mites exhibit a great variety of habits. They live principally on fluid 
nutriment, which is obtained from living plants or animals or from decaying 
organic matter. Many are free-living and predaceous, and large numbers are 
parasitic. The parasitic mites are of great interest on account of the wide variety 



THE ARTHROPODA 25 

of their habitats. Many, like the ticks, are external parasites of animals, feeding 
on the blood of their hosts; some, like many Sarcoptidae and Demodicidae, 
burrow in the skin of their hosts and cause severe itching and diseased condi- 
tions; others, such as Halarachnc spp. and Pneumonyssus spp., are found in 
the lungs of seals and Old World monkeys, respectively ; some, like the species 
of Trombidiidae, are parasitic in their larval stage (chiggers) but invariably 
free-living and herbivorous or predaceous as nymphs and adults. Many species 
attack birds and feed on the scales and feathers or even invade the lungs, air 
sacs, and hollow bones (as Cytoleichtts nudus) ; while others, such as the 
Tyroglyphidae, feed on stored food products, and man may be attacked by 
them when handling such material. Of still greater importance has been the 
discovery that many bloodsucking mites may serve as intermediate hosts of 
various pathogenic organisms of man and animals. In recent years the part 
played by the Acarina in the transmission of pathogenic organisms of man and 
animals has been studied by numerous investigators, and brief accounts of this 
work will be found under the discussion of the various groups. 

BRIEF SYNOPSIS OF THE ACARINA 

The Acarina is divided into a number of suborders (usually eight), based 
largely on the structure of the respiratory system. Five of these suborders 
contain mites that arc known to be parasitic and have some relation to man 
either as direct agents in producing diseased conditions or as vectors of patho- 
genic organisms. The classification of the order is far from satisfactory, but the 
following key will aid the student in placing parasitic forms: 

KEY TO THE SUBORDERS AND SUPERFAMILIES OF 
PARASITIC ACARINA 5 

1. Body vermiform, much prolonged behind; distinctly annulate or ringed; 

legs rudimentary and apparently composed of only three segments; pa- 
rasitic in the hair follicles or sebaceous glands of mammals 

Suborder BRACHYPODA 

There is only one superfamily Demodicoidea 

Body not vermiform, not prolonged behind; not parasitic in the hair 
follicles or sebaceous glands of mammals 2 

2. Tracheae present; spiracular openings two, one on each side of the body 

usually above the third or fourth coxa or a little behind them; spiracles 

5 There are more recent classifications, but this is more easily understood and should 
meet the needs of most workers in medical entomology. 



26 MEDICAL ENTOMOLOGY 

opening through distinct stigmatal plates Suborder MESOSTIGMATA 

2a. Hypostome large, furnished beneath with numerous recurved teeth; 

venter with furrows; skin leathery; large forms. (The ticks) .... 

Superfamily Ixodoidea 

2b. Hypostome small without recurved teeth beneath; venter without 

furrows but often with coriaceous shields 

Superfamily Parasitoidea 

Tracheae, when present, not opening through lateral spiracles 3 

3. Tracheae usually present, the spiracular openings near or at the bases 

of the chelicerae; larvae frequently parasitic, the adults free-living 

Suborder PROSTJGMATA 

33. Last segment of the palpus never forms a "thumb" to the preceding 

joint; body with few hairs Superfamily Eupodoidea 

3b. Last segment of the palpus forms a "thumb" to the preceding joint, 

which ends in a claw Superfamily Trombidoidea 

Tracheae, when present, not opening at the bases of the chelicerae 4 

4. Tracheae present; body divided into cephalothorax and abdomen, and the 

abdomen shows evidence of segmentation; females with a clavate hair 

between the first and second pair of legs Suborder IIETEROSTIGMATA 

This suborder contains one Superfamily Tarsonemoidea 

Tracheae absent; no division between cephalothorax and abdomen; ab- 
domen without true segmentation; females never with a clavate hair 

between the first and second pair of legs Suborder ASTIGMATA 

43. Surface of the body with fine parallel lines or folds; tarsi often pro- 
vided with stalked suckers; parasitic in all stages, chiefly on verte- 
brates Superfamily Sarcoptoidea 

4b. Surface of the body without fine parallel lines or folds; tarsi with- 
out stalked suckers; adults never true parasites 

Superfamily Tyroglyphoidea 

REFERENCES 
CRUSTACEA 

Calmen, W. T. The life of the Crustacea. New York, 1911. 

Essex, H. E. Early development of Diphyllobothrium latum in northern Minne- 
sota. Jl. Parasit., 14: 106-109, 1927. 

Fairly, N. H., and Listen, W. G. Studies on the pathology of dracontiasis. Ind. 
Jl. Med. Res., n: 922, 1924. 

Faust, E. C. Human helminthology. Philadelphia, 1939. 



THE ARTHROPODA 27 

Moorthy, V. N. A redescription of Dracunculus medinensis. Jl. Parasit., 23: 220- 

224, 1937. 
. Observations on the development of Dracunculus medinensis larvae in 

Cyclops. Amer. Jl. Hyg., 27: 437-460, 1938. 
, and Sweet, W. C. Further notes on the experimental infection of dogs with 

Dracunculus medinensis. Ibid., 27: 301-310, 1938. 

Smith, G. The Crustacea. In Cambridge Natural History, 4: 1-252, 1909. 
Vergeer, T. The broad tapeworm in America. Jl. Inf. Dis., 44: i-n, 1929. 
Ward, H. B. Animal parasites. In Abt's Pediatrics, 8: 912-1065, 1926. 
. Studies on the broad fish tapeworm in Minnesota. Jl. Amer. Med. Assoc., 

92: 389-390, 1929. 
Yoshida, S. On the intermediate hosts of the lung distome, P. wcstcrmanni Ker- 

bcrt. Jl. Parasit., 2: 111-118,1916. 

ARACHNIDA GENERAL REFERENCES 

Comstock, J. H. The spider book. Ithaca, N.Y., 1948. 

Emerton, J. H. The common spiders of the United States. Boston, 1902. 

McCook, C. American spiders and their spinning works. Philadelphia, 1889- 
1893. 3 vols. 

Warburton, C. Scorpions, spiders, mites, ticks, etc. In Cambridge Natural His- 
tory, 4: 297-473, i9 9- 

AC ARINA G EN ER AL REFERENCES 

Banks, N. A. Catalogue of the Acarina or mites of the United States. Proc. U.S. 

Nat. Mus., 32: 595-625, 1907. 
. The Acarina or mites. U.S. Dept. Agr., Office of the Secretary, Rept. 108, 

1915. 

Canestrini, G. Prospetto dell' Acarofauna italiana. Padua, 1885-1897. 7 parts. 
Ewing, H. E. A systematic and biological study of the Acarina of Illinois. Univ. 

111. Bull., Vol. 7, No. 17, 1910. 
. The origin and significance of parasitism in the Acarina. Acad. Sci. St. 

Louis, Trans., Vol. 21, No. i, 1912. 
Vitzhum, H. G. Acari. In W. Kiikenthal and T. Krumbach, Handbuch der 

Zoologie, 3 (zwcite Halite): i 160, 1931. 
. Acarina. In Bronns, Klassen und Ordnungen des Tierreichs. Funfter 

Band, IV Abteilung, 5 Buch, 1-3 Lieferung: 1-1011. Leipzig, 1940-1942. 



CHAPTER III 



The Order Acarina; Ixodoidea 



THE ticks constitute the superfamily Ixodoidea. They are readily distin- 
guished from all other mites by the possession of a pair of stigmatal plates 
(Figs. 4,5) situated laterally above, and usually posterior to, the fourth pair of 
legs. Furthermore their large size and leathery skin distinguish them from all 
other mites. The superfamily consists of two families the Ixodidae, in which 




Fig. 4. Dcrmacentor andcrsoni. Left: Dorsal view of male. Right: Ventral view of male. 
A, anus; AG, anal groove; BC, basis capituli; C. capitulum; Cr, cervical groove; E, eye; 
F, festoons; Ga, genital groove; GO, genital opening; Lg, lateral groove in scutum; 
S, scapula; Sp, spiracle; I-IV, the legs. 

the species are recognized by the presence oi a dorsal shield or scutum and the 
capitulum is located at the anterior margin and is visible from the dorsal sur- 
face, and the Argasidae, in which the do^al^shjelc^is absent and the capitulum' 
is ventral and rarely visible from the dorsal view (Figs. 12-14). The capitulum 
is a specialized organ and its structure is the most characteristic feature of 



THE ORDER ACARINA 29 

ticks. The group is not a large one in number of species. Probably not more 
than four hundred are known at present. In number of individuals, ticks are 
often very abundant, and constitute one of the most important groups of animal 
ectoparasites and vectors of diseases. All ticks are parasites of vertebrates and 
are most abundant on mammals and reptiles, though they are also common 
on birds and amphibia. Their food consists entirely of blood and lymph taken 
from their hosts. The life cycles of the various species of ticks differ greatly, 
some requiring only a single host, whereas others drop from their hosts after 
each feeding or remain on their hosts for two feedings and then drop of! 
(Fig. 20). Owing to their elastic, leathery skins, ticks, especially those belong- 




Fig. 5. Dcrmacentor andersoni. Left: Dorsal view of female. Right: Ventral view of 
female. A, anus; AG, anal groove; BC, basis capituli; Cr, chelicera; E, eye; F, festoons; 
Ga, genital groove; GO, genital opening; H, hypostome; Mg, marginal groove; P, palpus; 
Pr, porose areas; Sc, scutum; Sp, spiracle. 

ing to the family Ixodidac, can engorge an enormous amount of blood and 
increase greatly in size (Fig. 23). In general, ticks vary in size from less than 
2 mm. to nearly 25 mm. (some fully gorged females). 

Ticks are widely distributed throughout the world but are most abundant 
in the tropics and subtropics. Only two species, Ornithodoros moubata and 
O^rudis, are primarily restricted to man. Man is, however, used intermittently 
as a host by a rather large number of species. In recent years ticks have been 
shown to be the intermediate hosts and distributors of a large number of very 
important diseases of man and of domestic and game animals. Furthermore, 
tick bites arc known to produce rather serious effects, even death, in man and 
animals (lambs and calves, etc.). On account of these complicated interrela- 
tions ticks have become very important factors in public health and human 
welfare. 



30 MEDICAL ENTOMOLOGY 

MORPHOLOGY OF TICKS 
EXTERNAL ANATOMY 

THE IXODIDAE: The external structures of ticks are primarily adapted 
to meet the needs of parasitic life. The body is saclike, there being no divisions 
between the head, thorax, and jihdomgn- (Figs. 4,5) . It is somewhat depressed 
dorsoventrally, especially so in the imengorgecl tick and in the early stages. 
The body bears on the dorsum a shield or scutum, which varies in size and 
shape according to the species. In the female the shield is small, but in the 
male it almost covers the entire dorsal surface (Figs. 4,5). The eyes, when 
present, are located on or near the margin of the anterior half of the scutum 
(Figs. 4,5 E). There are four pairs of legs (in the larvae only three pairs are 
present). 

THE CAPITULUM. Located in an emargination, the camerostome, at 
the anterior end of the body is the specialized head, false head^or capitulum 
(Figs. 4,6). The basal portion, basis capituli (BC), consists 'of a rather broad, 
dense, sclerotized ring, constricted somewhat posteriorly to form a neck that 
fits into the anterior opening of the body cavity. Within and extending beyond 
the ring are the essential mouth parts concerned in piercing the host and 
extracting blood. The basis capituli varies in shape in the different genera 
of ticks; it may appear from the dorsal view as hexagonal, rectangular, or 
even triangular and may bear ridges, sharp angles, or other distinguishing 
characteristics. Females have a pair of depressions on the dorsal surface of the 
basis capituli. In these depressions lie the porose areas (Fig. 5 Pr), which consist 
of numerous open pores. They are of considerable taxonomic value, but their 
exact function is not known. 

THE PALPI OR PEDIPALPI: These structures arise from the lateroventral margin 
of the basis capituli. Each palpus consists of four segments (Fig. 6). The first 
segment is usually very short and not easily recognized when the capitulum 
is examined from the dorsal side. The second and third segments are longer, 
and the fourth segment is located in a deep pit or depression on the third. The 
fourth segment is usually furnished with a crown or row of stiff hairs, which 
may have a sensory function. In many of the Ixodidae the palpi are grooved 
along their inner face and form shields for the chelicerae and hypostome. The 
margins of the grooves are commonly supplied with long or short spines of 
various shapes (Fig. 6). 

THE HYPOSTOME: A dartlike structure, the hyjgostpme (Fig. 6 Hph), arises 
from the median ventral surface of the basis capituli and protrudes forward 



THE ORDER ACARINA 31 

directly beneath the mouth opening (Fig. 7 Hp). It consists of a basaljiortion, 
which is smooth and convex ventrally, and a distal portion, the ventral surface 
of which is provided with longitudinal rows of backward-projecting teeth. 
It is divided by a median fissure so that the teeth are separated into two series 
of files. The number of rows of teeth and the number of teeth in the rows 



Hph 



EA 




Fig. 6. Ventral view of capitulum of Dermaccntor andersoni. BC, basis 
capituli; CS, cheliceral sheath; EA, external article; Hph, hypostome; I A, in- 
ternal article; Pip, palpus (I-IV, segments of palpus) ; Sh, shaft of chelicera. 

differ in the various species and provide good characters for identification. 
The hypostome, when embedded in the tissues of the animal, acts as an effective 
anchor in maintaining the position of the tick. In fact, unless great care is 
exercised in removing ticks, the hypostome is frequently left in the host or a 
portion of the host's skin is removed with the tick. 

THE CHELICERAE: The chelicerae are the most important cutting organs of 



32 . MEDICAL ENTOMOLOGY 

the mouth parts, and their structure is complicated. They arise directly above 
the mouth opening and consist of a pair of cylindrical shafts, each lying within 
its sheath, the so-called "chelicera 1 sheaths" (Figs. 6,8). The sheaths arise as 
prolongations of the anterior margin of the basis capituli and lie in close contact 
with each other. The distal extremity of each sheath forms a flexible mem- 
brane, which invaginates and is attached to the chelicera directly behind the 
digits or articles (Fig. 8 CS). In this way the sheath forms a protection for the 
digits when they are withdrawn. The outer surface of the sheath, except 
the basal part, is usually covered with minute denticles, which give it the appear- 
ance of a fine file. Each ctiiej[iejra, the so-called "mandible," consists of a 



Ge 



Cl 



RM 




DM 



Fig. 7. Median longitudinal section through the capilulum of a tick to show the rela- 
tions of the internal and external parts. BC, buccal cavity; Cl, chelicera; D, digits of 
chelicera; DM, depressor muscles of capitulum FM, flexor muscles of the digits; Ge, 
Gene's organ; Hp, hypos tome; LM, levator muscles of capitulum; MO, opening into 
pharynx; O, opening of salivary duct; Ph, pharynx; RM, retractor muscles of chelicera; 
Sc, scutum; SD, salivary duct. (Diagrammatic; after Nuttall and Warburton, modified.) 

cylindrical shaft that bears at its extremity the chelate digits (Figs. 6,8). The 
shaft is very long and projects backward beyond the basis capituli into the 
body. The proximal part is dilated and to it are attached the retractor muscles 
of the chelicerae. The distal portion is more heavily sclerotized and bears at 
its extremity the digits or articles (Fig. 8). The articles are usually two 
in number: an internal digit with sharp cutting teeth articulated directly with 
the shaft and activated by two powerful tendons an internal one and an ex- 
ternal one arising from the mass of muscles within the shaft, and an external 
digit articulated with the internal digit and provided with sharp, pointed cusps. 
It is these organs that cut and lacerate the tissues of the host. A brief account 
of the method of feeding is given later. 



THE ORDER ACAR1NA 



33 



THE BODY: The dorsal portion of the body bears a scutum or ^shield. In 
the males the scutum covers practically the entire body surface (Fig. 4) ; 
in the females (Fig. 5) the scutum varies greatly in size and shape so that 
it serves as a means of distinguishing the different species. It never covers 
more than a small part of the dorsal surface. The scutum may be ornamented 
or plain (Figs. 4,5,9), and it bears 
furrows or grooves. The anterior 
margin is usually deeply emar- 
ginate; the lateral angles project 
forward and are called the scapu- 
lae (Fig. 4 s). On the dorsal 
surface of the scutum and body 
are several grooves that are of 
considerable significance. These 
are: (i) the cervical grooves that 
extend from the inner angles of 
the scapulae backwards on the 
scutum (Fig. 4 Cr); (2) lateral 
grooves that extend along the 
sides of the scutum in the males 
(Lg) ; (3) marginal grooves, ex- 
tending longitudinally near the 
lateral margins of the body in 
the females (Fig. 5 Mg). The 
scutum may be marked with 
shallow or deep punctures. On 
the sides of the scutum, either 
on the edge or just inside it, are 
the eyes, small globular clcva- 



cs 






Sh- 






ET- 


[ 




FT- 


. 


r 
11 






w 




. 8. Dcrmaccnto 
chelicera, ventral vie 



tions (Figs. 4,5). Injmany ticks greatly enlarged to she 



the eyes are lacking. 
The ventral surface presents 



Art, points of articuh 



mdcrsoni. Left: A single 
Right: Tip of chelicera 
w the articles, ventral view, 
ion of the internal article 
iff; CS, cheliceral sheath; 

~, 131', dorsal process of internal article; EA, exter- 
some important structures. The nal arlldc . ,. r rclr ltlor rendoll of internal ani 

legs are prominent features and cle; FT, flexor tendon of internal article; IA, in- 
are numbered I, II, III, and IV tc ; rnal articlc | M . muscles, Sh, shaft of chelicera; 
.. \ i i T 1 ' tendons of retractor muscles of chelicera. 

(Fig. 4), beginning at the ante- 
rior end. Directly behind the basis capituli will be found the opening of 
the genital organs in both the males and females (Figs. 4,5 GO). 1 Kxtending 

1 The genital opening is usually located between the first or second pair of legs, though 
in the genus Jxodcs it is found between the third pair of legs. 



34 



MEDICAL ENTOMOLOGY 




Fig. (}. Ticks. From the top down: Dermacentor variabilis, the dog tick; Haema- 
phy salts leporis-palustris, the rabbit tick; Rhipicephalus sangutneus, the brown dog 
tick. Males are at the left, females at the right. (After the U.S. Bureau of Entomology.) 



THE ORDER ACARINA 



35 



backwards from the genital orifice are a pair of grooves, the genital grooves 
(Figs. 4,5 Ga). These curving grooves extend to the posterior margin in 
nearly all species. Between the genital grooves in the median line and usually 
far behind the fourth pair of legs is the anal opening. Directly behind the 
anal opening is the anal groove, the convexity directed backward. This groove 
is present in all species of the Ixodidae except in the genera Boophilus and 




Fig. JO (lejt and center). Ventral view of Ixodcs ricinus, male; Ixodes coofyci, female, 
ventral view. A, anus; Ag, anal groove; AP, anal plate; AAP, adanal plate; Gg, genital 
groove; GO, genital orifice; H, hypostome; MP, median plate; P, palpus; PP, pregenital 
plate; Sp, spiracle. 

Fig. 11 (right). (/) Fourth leg of Dermacentor andersoni. (2) Tarsus of the first leg, 
showing Mailer's organ (ho), c, coxa; f, femur; pt, protarsus t, tarsus, ti, tibia; tr, tro- 
chanter. 

Ixodes. In Boophilus the groove is lacking, whereas in Ixodes the groove 
surrounds the anus in front (Fig. 10) . On the ventral surface of the males of the 
genera Ixodes, Boophilus, and Rhipicephalus there are various types of scle- 
rotized shields. In Ixodes these shields or plates appear as nonsalient struc- 
tures, and definite names have been applied to them (Fig. 10). In the other 
genera the plates are more or less raised and usually consist of two pairs, 
the adanal and accessory shields. 

Behind and above the coxae of the fourth pair of legs are the spiracles. They 
are located on sclerotized stigmatal plates (Figs. 4,5,10). The stigmata are of 
various shapes, circular, oval, triangular, comma-shaped, etc. The spiracular 
openings are present in the nymphs and adults but are lacking in the larvae. 

THE LEGS : Ticks, in the adult and nymphal stages, possess four pairs of legs. 
The larvae have only three pairs (Fig. 19). Each leg consists of the following 
parts: (i) Thcjcoxa. This is the basal portion and is firmly and immovably 



36 MEDICAL ENTOMOLOGY 

attached to the body wall. It is often armed with spines, spurs, or teeth (Fig. 
n). (2) The trochanter. This is attached to the coxa by an intersegmental 
membrane. It is usually very short and has a somewhat rotatory movement 
in its socketlike depression in the coxa. (3) The femur. Following the tro- 
chanter is the stout, rather short femur. It is usually smooth or provided with 
a few hairs or spines. (4) Thcjibia. This is sometimes called the patella and 
is rather short and stout. (5) The protarsus. The tibia is followed by the 
protarsus. (6) The tarsus. The last segment, the tarsus, which is attached to 
the protarsus, has frequently a pseudoarticulation, indicating a two-jointed 




Fig. 12. Ornithodoros moubata. Left: Ventral view. Right: Dorsal view. C, capitulum; 
Dh, dorsal humps; GO, genital opening. (Redrawn from Nuttall and Warburton.) 

condition. (7) The claws. The tarsus bears the claws, which are located on a 
stalk. (8) The : rjujyjllus. Lying between the claws is the pulvillus, which may 
be present or absent (Fig. n). 

On the tarsus of the first pair of legs is a peculiar organ (Fig. 11 ho) that 
should not be overlooked. This is the so-called Hallgr's organ. It consists of a 
small vesicle containing sensory hairs. Its cavity is connected with the exterior 
by a minute pore. Hinclle and Merriam (1912) have definitely established 
that this organ has an olfactory function. 

THE ARGASIDAE: The external anatomy of the Argasidae differs from 
that of the Ixodidae. The scutum or dorsal shield is lacking, and on this 
account the Argasidae have been called the "soft ticks." The capitulum is 



THE ORDER ACARINA 



37 



located on the ventral surface, just behind the anterior margin (Figs. 12,13). 
Porose areas are absent. The appearance of the dorsal surface of an argasid tick 
is markedly different from that of an ixodid tick. (Cf. Figs. 4,5 and 12-14.) 
The ventral surface possesses somewhat similar structures, but the arrange- 
ment of the grooves is often quite different (Fig. 14). The spiracles are located 
just above and in front of the fourth pair of coxae. The stigmatal plate is usually 
small and not so heavily sclerotized (Fig. 15). Eyes, when present, are ventral 
in position and are located on longitudinal ridges just above the coxae. Probably 





Fig. i}. Argas persicus. Dorsal and ventral views of female. (After Bishopp.) 

one of the most striking differences in the external anatomy is the leglike 
character of the pedipalpi or palpi (Fig. 16). These organs closely resemble 
the homologous structures in spiders and indicate the more generalized char- 
acter of the argasid ticks. The structure of the legs is similar to that of the 
Ixodidae except that the pulvillus is very small or lacking and the coxae are 
unarmed (without spines or teeth) . 

INTERNAL ANATOMY 

The internal anatomy has been studied by a number of investigators. A 
brief resume is here presented in order that the student may understand the 
main structures concerned with digestion, respiration, and reproduction. The 



MEDICAL ENTOMOLOGY 




^V^ 3 

Fig. 14. Ornithodoros species. (/) Ventral and dorsal views of 0. talaje. (2) Ventral 
and dorsal views of 0. hermsi. (3) Same of 0. tuncata. (4) Same of 0. parkcri. G, genital 
opening; Ga, genital groove; P, preanal groove; Ta, transverse postanal groove. (All after 
Cooley.) 



THE ORDER ACARINA 



39 



mouth parts have already been described. It is now necessary to indicate their 
function and the method of obtaining blood. The tick, placed on its host, pro- 
ceeds to attach by breaking the skin with the sharp cutting articles situated 
at the ends of the cheliceral shafts. The articles, controlled by powerful muscles, 
soon lacerate the tissues, and the hypostome is forced into the wound. The 
strong recurved teeth of the hypostome are firmly embedded and are forced 
deeper and deeper as the chelicerae cut the tissues. Soon the entire capitulum, 
except the palpi, which never enter the wound, are deep in the flesh of the 
host. 



Palp article^ 





Fig. 75 (Jcjf). Argas pcrsicus. Spiracle. (After Nuttall.) 

Fig. 16 (right). Capitulum of Argas persicus. (After Nuttall.) 

Once the tick is attached, the blood is extracted by means of a powerful 
pumping pharynx (Figs. 7,17). The buccal cavity lies between the palpi within 
the anterior part of the basis capituli and above the hypostome. It is tubelike 
and ends posteriorly in a small bayou, widened out laterally, into which open 
the salivary ducts. The secretion of the salivary glands has been shown, in 
some cases, to possess an anticoagulin and enables the tick to obtain a steady 
flow of liquid nourishment. Leading from the floor of the buccal cavity at its 
posterior end is the short pharynx. 

Sen (1935, 1937) describes a peculiar structure ("stylet") overlying the 
entrance to and at the anterior end of the pharynx. Bertram (1939) apparently 
refers to the same structure as the tongue, and Arthur (1946) describes it in 
detail. According to Bertram and Arthur, this structure closes the entrance 
to the pharynx when the muscles of the pharynx contract to force the blood 
into the esophagus. It thus prevents the backflow of the blood into the wound. 

The pharynx is a chitinous tube richly supplied with dilator and contractor 
muscles. It terminates in the thin-walled, short esophagus, which passes 



40 MEDICAL ENTOMOLOGY 

through the brain and thence to the stomach or mid-intestine. The mid- 
intestine (Fig. 17 St) consists of a short, thin tube with numerous large 
diverticula. The diverticula generally arise at the anterior and posterior ends 
of the mid-intestine. Their number, length, and shape vary in the different 
species. These diverticula are capable of great distension and enable the ticks 
to extract a large amount of blood at one feeding. Ticks which drop oft their 
hosts at each feeding are thus furnished with a food supply that enables them 
to withstand long periods of starvation. The hind intestine arises from the 
lower surface at the posterior end of the mid-intestine. It appears as a delicate 
white cord and is supposed to be largely functionless in most ticks. In some, 
like Argas persicus, discharges of wastes take place, but in the great majority 
of ticks excretion probably occurs through the Malpighian tubules, skin, and 
other organs. The hind intestine terminates in a saclike rectum. A single 
Malpighian tubule arises from each side of the rectum. Each tubule is long 
and winds about and among the internal organs. Each is more or less filled 
with a whitish substance, which is evacuated through the rectum. These 
tubules are probably excretory organs. 

The salivary glands, two in number, lie in the anterior portion of the body, 
extending backward on each side to the base of or beyond the third pair of 
legs (Fig. 17 Sga). Each gland appears like a small bunch of grapes and is 
composed of rather large secretory cells that pour out their secretions through 
an independent duct. Each duct opens near the base of the buccal cavity. An- 
other pair of glands that appear to have considerable importance and about 
which little is known are the coxal glands. These open near the base of the 
first pair of coxae. They are known to discharge a secretion while or just 
after feeding (Argas and Ornithodoros). The exact function of these glands 
has not yet been determined. It is known, however, that certain spirochetes are 
transmitted to new hosts by means of the fluid from these glands (e.g., Ornitho- 
doros moubata and relapsing fever). 

The reproductive system of the female consists of a duplex ovary located 
just above the posterior end of the mid-intestine. The ovary extends across 
the body, and each end terminates in an oviduct. The oviduct from each side 
runs forward as a long coiled tube. The oviducts unite at their anterior ends 
to form the uterus (Fig. 17) . From the uterus the vagina leads to the external 
orifice (Figs. 5,12). Surrounding the vagina are various glands that are active 
at the time of egg laying. 

The male reproductive system consists of a duplex testis occupying a posi- 
tion similar to that of the ovary in the female. A vas deferens extends forward 
from each end of the testis. These unite near the external orifice. The sperm 



THE ORDER ACAR1NA 



Fc 



GO 



-- VOa 




Mt 



Fig. 77. Argas persicus. Ventral view of dissection of young female. The left side of the 
figure represents internal organs as they appear after removal of integument; on the 
right side part of the stomach and intestinal caeca have been removed. B, brain; Cl, cheli- 
cera; Fc, occipital foramen; Ga, glandular part of Gene's organ; GC, caeca of gut; 
GO, Gene's organ; H, heart; M, muscles of chelicera; Mt, Malpighian tubules; O, esopha- 
gus; Ov, ovary; Ph, pharynx; R, rectum; S, rectal sac; Sga, salivary gland; Sp, spiracle; 
St, stomach; UT, uterus. (Adapted from Robinson and Davidson.) 



42 MEDICAL ENTOMOLOGY 

collects in a lobular swelling (seminal vesicle) situated near the junction of the 
vasa deferentia. Here, in a complicated manner, the spermatozoa are formed 
into spermatophores. 

Another organ that requires description is Gene's organ. It is associated with 
egg deposition (Fig. 7, Ge). In the Ixodidae it is located directly beneath the 
scutum and opens to the exterior between the scutum and the basis capituli; in 
the Argasidae it is just in front of the capitulum. Gene's organ is glandular in 
structure, is present only in the females, and becomes functional at the time 
of egg deposition. 

The structure of the other internal organs need not concern us here. Full 
details may be obtained by consulting the references. 

SYNOPSIS OF THEJXODOIDEA 

The Ixodoidea contains two families, the Argasidae and the Ixodidae. The 
families may be separated by the following key : 

1. Scutum lacking; capitulum ventral, usually concealed beneath the anterior 

margin, and always subterminal; body alike in both sexes (Fig. 14) 
Argasidae 

2. Scutum present; in the males the scutum extends over the entire dorsal 

surface; in the females, nymphs, and larvae only on a portion of the 
anterior dorsal surface; capitulum terminal and always visible from the 
dorsal surface (Fig. 9) Ixodidae 

THE FAMILY ARGASIDAE 

The family Argasidae consists of those ticks that lack a scutum, the so-called 
"soft ticks." There is very little sexual dimorphism, the males closely resem- 
bling the females. The capitulum is always inferior, and the spiracles are small 
and located anterior to coxa IV. In the adults the integument is leathery, 
wrinkled, granulated, mammillated, or provided with tubercles. The palpi 
are free and all the segments are freely movable. The porose areas are absent. 
The adults, even when engorged, never increase greatly in size; when fasting 
their flattened appearance bears some resemblance to bedbugs. Their principal 
hosts are birds (especially poultry), domestic animals, rodents, bats, and man. 
They are found commonly in the habitats of their hosts as in rodent burrows, 
bat roosts, poultry houses, caves, and human abodes as well as on the ground 
where they drop from their hosts. They appear to be chiefly nocturnal in their 
feeding habits. There are only four well-recognized genera: Argas, Ornitho- 
doros, Antricola, and Otobius. 



THE ORDER ACARINA 43 

KEY TO THE GENERA OF ARGASIDAE 

1. Margin of the body thin and acute; a sutural line separating the dorsal 

and ventral surfaces (Fig. 13) Argas 

Margin of the body not thin and acute, but if so no sutural line separating 
the dorsal and ventral surfaces (Fig. 14) 2 

2. Nymphs with the integument beset with spines; hypostome well devel- 

oped; adults with the integument granular; hypostome vestigial Otobius 
Nymphs with the integument not beset with spines; mammillated or 
tubercular; hypostome not vestigial in either nymphs or adults 3 

3. Hypostome scooplike on dorsal surface, broad at base. (Known from 

bats; only 2 species) Antricola 

Hypostome never scooplike on dorsal surface, not so broad at base. (On 
various classes of animals including bats and man; a large genus) .... 

Ornithodoros 

The genus Argas Latr. contains only a few species, but some of these are 
world-wide in distribution. The following key will aid in the identification of 
the common species : 

1. Body nearly circular, discoidal vespertilionis Latr. 

Body not circular, longer than broad 2 

2. Margin of body striate 3 

Margin of body not striate, marked of? by distinct quadrangular "cell- 
like" plates (Fig. 13) persicus Oken 

3. Body subconical in front; dorsum marked with polygonal depressed areas; 

large species, 15 by 10 mm. (Known from East Africa) . . brumpti Neum. 
Body rounded in front; dorsum marked with fine wrinkles and discs as in 
persicus (species not so large). (Parasitic on pigeons and widely dis- 
tributed in Europe, North Africa, and northern South America; re- 
ported from the U.S.A.) reflexus Fabr. 

The genus Ornithodoros Koch contains many important species that attack 
man and act as vectors of serious diseases. They occur in many parts of the 
world, but none of the species is known to be world-wide in distribution. 
Nuttall (1908) listed only n well-established species, but at present nearly 50 
species have been described, though some of them are of doubtful validity. 

KEY TO THE MORE COMMON SPECIES OF ORNITHODOROS 

i. Cheeks present (flaps at sides of camerostome) 2 

Cheeks absent 5 



44 MEDICAL ENTOMOLOGY 

2. Tarsi with humps (Fig. 12) though they may be small. (From Brazil) 

brasiliensis Aragao 

Tarsi without humps 3 

3. Tarsus IV with long subapical protuberance 

tholozani (Labou. and Megn.) 

Tarus IV without long subapical protuberance 4 

4. Discs large and easily seen. (Southern U.S.A. south to Argentina) 

(Fig. 14) talaje Guerin-Men. 

Discs very small and inconspicuous. (Known only from human abodes; 
Panama, Colombia, and Venezuela) rudis Karsch 

5. Integument not strongly mammillated, appearing more or less wrinkled; 

dorsum with discs, two elongate, parallel discs near front being distinc- 
tive. (India, Persia, Russian Turkestan, Palestine) . . lahorensis Neum. 
Integument strongly mammillated; discs present or absent but lacking 
the two described above 6 

6. Eyes present 7 

Eyes absent 8 

7. Anterior eyes much larger than posterior. (Pacific coast of U.S.A., Cali- 

fornia to Mexico) coriaceus Koch 

Anterior and posterior eyes about equal in size. (Arabia, Africa, India, 
Ceylon) savignyi Aud. 

8. Dorsal humps present on all tarsi and prominent (Fig. 12 Dh) 9 

Dorsal humps, when present, not on all the tarsi 10 

9. Tarsus IV with three humps. (Hot dry areas of Africa from Lake Chad 

east and south to Cape Colony) moubata Murray 

Tarsus IV with one apical hump or the hump might be considered the 
apical protuberance. (Southern Brazil, Argentina, Paraguay, and 

Bolivia) rostratus Aragao 

10. Tarsi bifurcate and with dorsal humps. (Algeria) foleyi Parrot 

Tarsi not bifurcate and without humps on all or some of the tarsi n 

u. Dorsal humps absent from all the tarsi. (Western United States.) (Fig. 

14) hermsi Wheeler, Herms, and Meyer 

Some of the tarsi with dorsal humps 12 

12. Dorsal humps on the tarsi very long; tarsus IV with subapical protuber- 

ance or hump; mammillae very large and coarse. (Southern Brazil, 

Argentina, Paraguay, and Bolivia) rostratus Aragao 

Dorsal humps not so long: mammillae not so large and coarse 13 

13. Tarsus IV without dorsal humps but with subapical protuberance. 

(Mexico) nicollei Mooser 



THE ORDER ACARINA 45 

Tarsus IV without dorsal humps and without subapical protuberance . . 14 
14. Mammillae large (Fig. 14), relatively few and not crowded. (South- 
western United States, Florida, Mexico) turicata Dugcs 

Mammillae small (Fig. 14), crowded, and numerous. (Western United 
States) par\eri Cooley 

The genus Otobius contains only two North American species. O. megnini 
is the "spinose ear tick" of cattle and horses and has been recorded from man. 

0. lagophilus Cooley and Kohls is reported only from cottontail rabbits and 
jack rabbits from the western United States and Canada. Both species can be 
easily recognized as nymphs by their spinose integument. The genus Antricola 
occurs on bats or in bat roosts. Only two species are known, both from the 
Americas. 

THE FAMILY IXODIDAE 

The family Ixodidae contains those ticks that have a scutum or shield and 
have been called the "hard ticks." Sexual dimorphism is marked, the males 
being completely covered on the dorsum by the scutum and incapable of great 
distention; the females may become greatly enlarged when engorged, and the 
scutum appears as a small shield behind the capitulum. The capitulum is 
always terminal, and, in the females, porose areas are present. This family 
contains the great majority of ticks and is world- wide in distribution. Their 
principal hosts arc mammals, reptiles, amphibians, and birds. It is not possible 
to give an adequate key to all the described genera as some of them are rare 
and not well known or studied. 

KEY TO THE PRINCIPAL GENERA OF IXODIDAE 

1. Anal groove surrounds the anus in front (Fig. 10) ; eyes absent. (World- 

wide in distribution) Ixodes 

Anal groove curves about the anus posteriorly (Fig. 4) or is absent; eyes 
present or absent 2 

2. Eyes absent 3 

Eyes present .4 

3. Inornate; festoons present; palpi short, conical when closed and segment 

2 projects laterally (except in rare cases) beyond the basis capituli (Fig. 

9) ; coxa I never bifid. (Distribution world-wide) Haemaphy salts 

Ornate; palpi long, segment 2 especially long; festoons present. (Occur 
mainly on reptiles; tropical and subtropical) Aponomma 

4. Anal groove absent or very indistinct; inornate; eyes present and mar- 



46 MEDICAL ENTOMOLOGY 

ginal; festoons absent; palpi very short, second and third segments com- 
pressed and ridged dorsally and laterally; males with adanal and acces- 
sory shields. (Tropical and subtropical) Boophilus 

Anal groove present and distinct; ornate or inornate but without all of the 
above combination of characters 5 

5. Ornate; eyes and festoons present; eyes marginal; abdomen without a 

pair of terminal protrusions capped by sclerotized points 6 

Inornate, but if ornate (rarely in Hyalomma and Rhipicephalus) with a 
pair of abdominal protrusions capped by sclerotized points 7 

6. Palpi short; second palpal segment not twice as long as wide; hypostome 

with the denticles arranged in 6 rows, 3 on each side (expressed as 
3/3) and occupying most of its length. (Distribution world-wide) . . 

Dermacentor 

Palpi long; sec % ond segment twice as long as wide; hypostome with 
denticles largely restricted to the apical half and arranged usually 3/4 
or 4/4. (Tropical and subtropical) Amblyomma 

7. Eyes not on the margin of scutum but moved inward; if ornate with 

a pair of abdominal protrusions capped by sclerotized points. (Old 

World, tropical and subtropical) Hyalomma 

Eyes located on margin of scutum; without the abdominal protrusions . 8 

8. Ventral plates or shields absent in both sexes 9 

Ventral plates or shields present in the males, absent in the females; basis 

capituli usually hexagonal in dorsal view. (Distribution world-wide) . . 
Rhipicephalus 

9. Basis capituli rectangular in dorsal view; coxae not increasing greatly in 

size from I to IV; coxa IV without spines; spiracles subcircular. (Tropi- 
cal America) Otocentor 

Basis capituli hexagonal in dorsal view; coxae increasing greatly in size 
from I to IV; coxa IV with very long spines; spiracle comma-shaped. 
(Africa) Rhipicentor 

Over three hundred species of ixodid ticks have been described. It is not 
possible to give keys to the species included in the different genera. In the 
bibliography will be found references in which keys to the species of certain 
genera are given. These references are indicated by a dagger. The genus 
Dermacentor contains species important as transmitters of human diseases, 
and the following key will aid in recognizing the North American species. 



THE ORDER ACARINA 

KEY TO THE IMPORTANT AMERICAN SPECIE^ 
DERMACENTOR 

1. Spurs on coxa I diverging from their base outwards. (Southwestern U. 

Texas to Oregon; hosts mainly rabbits) parumapertus Neui, 

Spurs on coxa I with proximal edges closely parallel or slightly diverg- 
ing near apices 2 

2 . Spiracular plate oval, without dorsal prolongation and with goblets few 

and large. (Widespread in North America) albipictus Pack. 

Spiracular plate oval, with dorsal prolongation and the goblets numerous 
or moderate in numbers 3 

3. Cornua long, especially so in the males. (West coast from Oregon to 

southern California) occidentalis Marx 

Cornua short or of moderate length 4 

4. Goblets of Spiracular plate very small and numerous. (Eastern North 

America to Saskatchewan south through central Texas) . . variabilis Say 
Goblets of spiracular plate large and not so numerous or densely packed. 
(Western North America, Saskatchewan to British Columbia south 
to northern New Mexico) andersoni Stiles 

BIOLOGY OF TICKS 

Ticks are all external parasites of mammals, birds, reptiles, and some am- 
phibia. During their life cycles they pass through four stages egg, larva, 
njmphj and adult. All species oviposit on the ground or in the habitats of 
their hosts, usually in sheltered places (Eig. 18). The time required for the de- 
velopment of the embryo within the egg varies widely not only with the species 
but also with temperature r moisture, and other_climatic factors. The hexapod 
^LYf* (fig* I 9)>. which hatches from the egg, is very active (there are a few 
known exceptions) and seeks out its host in various ways. After feeding, the 
larva drops oft and molts on the ground or remains on its host an3 molts. 
Thejiymph, the next stage, possesses eight legs, and the tracheal system with. 
ksjsiracles (lacking in the larva) are now present. The external opening of 
the genital organs is still lacking. After another feeding the nymph again 
leaves its host and molts, or it may. remain. aa.d..mQl.t.. on theJiQ&t. This js, the. 
adult stage, which is usually quite similar toj^^of^l^jiyjiir^^ 
the external genital ^>nfice ' ls present. In the Argasidae there may be several 
nymphal stages, but all ticks of the family Ixodidae have, as far as known, 
only a single nymphal stage. The adults arc not known to molt but feed and 



MEDICAL ENTOMOLOGY 

A r hosts or on the -ground. Shortly after mating the ; 

. In the Ixodidae the males usually die shortly after matinj 

> after laying their batches of eggs. In the Argasidae the adults are 

_,-lived, the males and females living for a long time, even several years. 

.gg laying usually takes place after each blood meal. 

Though the above statement represents the general life cycle of ticks^each 

species undergoes its own peculiar developmental cycle. Some ticks complete 

their life cycle on a single host 3 molting and mating without leavmg~diiC'ri0sT;" 

such ticks arc known as one-_host jicks, as Boophihts anniilatus and Demia^ 

centor albipictus; some require two hosts, as Rhipiccphalus evertsi and 




Fig. 1 8 (left). Dcnnaccntor albipictus. Female laying eggs. (After Department of 
Agriculture, Division of Entomology, Canada.) 
Fig. 79 (right). Boophilus annulatus. Recently hatched larva. (After Cotton.) 



f and arc^ called two-host ticks; many others require 
three hosts, dropping off after each feeding, and are known as three-host ticks, 
as Dermacentanund.cr-SQni, D. variabilis, and many other species; and still other 
ticks require even more hosts, as many of the argasid ticks such as Argas 
pcrsiats, Ornithodoros monbata, and 0. savignyi, and may be called many- 
host ticks. The relation of ticks to their hosts is shown graphically in Fig. 20, 
and nearly all the known types of life cycles are indicated. 

Sexual reproduction occurs generally in ticks, though Aragao (1912, 1936) 
and Brumpt (1924) have shown that Amblyomma rotundatum (agamun) 
probably reproduces normally parthem genetically. Mating takes place, in 
most cases, on the host, the male seeking out the female. In all species so far 
described, the male attaches beneath ihc female and uses his mouth parts as an 



THE ORDER ACARINA 



Second nymphal stage attacks hoat III 
Nymphs drop off when replete 



Second nymphal stage when replete 
drops to the ground 




Fig. 20. Life cycles of ticks. The black areas (sectors) represent the periods of blood 
taking. Type I: Argas persicus, Argas reflexus (?), Ornithodoros sp. Type II: Ornitho- 
doros monbata, O. savignyi. Type III: Ixodes ricinus, I. hcxagonus, I. canisuga, Derma- 
centor reticulatus, D. occidcntalis, D. variabilis, D. andersoni, Haemaphysalis leacht, 
H. punctata, II. kporis-palustris, Amblyomma hebraeum, A. maculatiim, A. cajennense, 
A. americanum, Rhipiccphaltts appendiculatus, R. sanguineus, R. sinnts. Type IV: Rhi- 
picephalus evert si, Hyalomma acgyptium. Type V: Boophilus annulatus, B. dugesii, 
Dermacentor albipictus. Type VI: Otobius mcgnini. (There are other types of life cycles 
not shown on the chart.) 

external genital organ. After the male has distended the vulva of the female 
with his mouth parts, he moves forward until his genital orifice is directly 
over that of the female. Then with great rapidity a viscid spermatophore is 
applied to the vulva and is promptly received by the female. The females may 
mate several times with different males. 



50 MEDICAL ENTOMOLOGY 

Egg deposition in ticks is a rather remarkable performance. The eggs are 
always found in front of the female (Fig. 18), whereas the genital opening is 
on the ventral surface (Fig. 5). The transfer of the eggs is accomplished in 
the following manner: When ready to oviposit the female withdraws the 
capitulum as far as possible within her body and Gene's organ is extruded. 
The vulva is partially everted, and an egg is protruded and rolled around until 
it comes in contact with the sticky Gene's organ; when this is done the organ"" 
is withdrawn, and the egg is carried to the dorsal surface and pushed off in 
front of the tick. This process is repeated for each egg. That it must be a 
laborious procedure is evident when it is remembered that some ticks lay as 
many as 12,000 eggs. The secretion of Gene's organ is believed to be protective. 

Many ticks are known to be long-lived and to be able to withstand long 
periods of starvation. Various larvae are known to live seven or eight months 
or even longer without any food; adults of Ornithodoros moubata have sur- 
vived without food* for over a year; O. savignyi for over two years; O. hennsi 
for four years; Argas persicus for three or four years; A. reflexus for five years; 
Dermacentor andersoni at least four years. Many other species of ticks have 
been kept alive without food for varying lengths of time. Ruttledge (1930) 
kept a female of Argas brumpti (collected in the wild) alive for nearly 12 
years; Francis (1938) kept Ornithodoros turicata alive for five years unfed 
and infected with spirochetes of relapsing fever; another group he kept alive 
unfed for four years, and then they infected a monkey with relapsing fever; 
two and a half years later the same group fed on a monkey and infected it 
with relapsing fever, demonstrating six and a half years of natural infection. 
In 1942 Francis records the maximum length of life of this tick under experi- 
mental conditions as 9 years 10 months and 7 days. 

SPECIAL BIOLOGIES 

Owing to the importance of ticks as vectors of human and animal diseases 
a few of the life histories of the more important species need to be given 
in some detail. 

THE FAMILY ARGASIDAE 

THE GENUS ARGAS: Argas persicus (Oken) is the common fowljick 
(Fig. 13). The males and females appear very similar but may be separated 
by the shape of the genital opening. In the males the genital opening appears 
crescent-shaped, whereas in the females it is a narrow transverse slit. The 
mature female, unengorged, measures from 5 to 8 mm. in length and the 



THE ORDER ACARINA 51 

male from 4.5 to 6 mm. The domestic fowl is the principal host, though turkeys, 
geese, and ducks are attacked; wild birds are also frequent 



is occasionally attacked when associated with ppu|try. 

The fowl tick has a world-wide distribution and occurs in the warm and dry 
regions of Europe, Asia, Africa, the Americas, and Australia. The distribution 
in North America is shown in Fig. 21. In our warm poultry houses it fre- 
quently occurs far north of its range, as in Baltimore, Maryland. 

The mature males and females feed at night and become engorged in less 
than an hour. Dropping from their hosts they seek shelter in any convenient 
hiding place. The females deposit a batch of eggs after each blood meal, and 
each female may lay several batches of eggs. Over 600 eggs are laid by the 
average female. The eggs hatch in from 10 days to several weeks. The larvae 
attach to their hosts and become engorged in about 5 days. They drop from 
their hosts and molt to the first nymphal stage in about a week. The first-stage 
nymph now feeds at night, and a second molt takes place in about another 
week. Another molt occurs about a week later, and the third-stage nymph 
after feeding usually molts to the adult. The entire life cycle from egg to adult 
may be completed in about 30 to 40 clays if food and warmth are suitable. This 
tick is a serious pest of poultry, killing young birds in large numbers. It is the 
vector of a serious disease of fowls, spirochetosis, caused by Spirochaeta gal- 
linarum Blanchard (S. marchouxi Nuttall). Recently (1943) it has been 
reported capable of transmitting anaplasmosis of cattle. It or a closely allied 
species, Argas mianensis, is said to attack man commonly in Persia and 
produces a fever known as Mianeh fever. 

Argas reflcxus (Fabr.) is primarily a parasite of pigeons and occurs most 
commonly in the Old World. It also occurs in northern South America, and 
Cooley (1944) records a few localities in the United States. Why it has not 
spread among pigeons in this country is not known. A. bntnipti Neum. is our 
largest known argasid tick, measuring nearly 20 mm. in length. It has been 
taken only in East Africa (Somaliland, Kenya, and the Sudan). A. vesper- 
tilionis (Latr.) is a beautiful nearly circular tick; it is recorded from bats in 
England, Europe, North Africa, South Africa, southern India, and Australia. 
Patton and Cragg reared this species on bats in India; it completes its life 
cycle in about two months. 

THE GENUS ORN1THODOROS: Many species of this genus are im- 
portant agents in the transmission and dissemination of human diseases. Only 
a few of the species can be discussed here. 

Ornithodoros moubata (Murray), the eyeless tampan, is probably the best 
known tick (Fig. 12) that prefers man as its host in all stages. It also feeds on 



52 MEDICAL ENTOMOLOGY 

pigs, goats, dogs, shrrp, an d other domesticated animals. It is found only in 
Africa, where it is widely distributed in the hot dry areas from Lake Chad 
eastward to the Red Sea and south to the Cape Province. It is also reported 
from northwestern Madagascar. Here they are found most commonly in the 
rest houses along the caravan routes, in native huts, and in the village houses. 
The ticks prefer the dry places such as about hearths and bed platforms, in the 
cracks and crevices of the mud floors, in the dry grass walls, and about the 
doorsills. The females lay their eggs in batches at night, placing them in 
cracks and crevices or in hollows made in the ground. Each female normally 
lays several batches of eggs, a batch after each blood meal. Jobling (1925) 
records each female as laying from 600 to over 1200 eggs. The eggs hatch in 
from eight days to two or three weeks. The larvae, however, do not leave the 
eggs but remain within the shells and molt to the nymphal stage in about four 
days. According to Jobling, the males undergo four molts and the females 
five molts before -reaching maturity. Both the nymphs and adults are noc- 
turnal and feed primarily at night. The nymphs require about a half-hour 
to become engorged and then drop from their hosts. The adults are long-lived 
and can live for several years. This tick is the important vector of African 
relapsing fever throughout its range., 

Ornithodoros savignyi (Aud.), the eyed tampan, closely resembles 0. mou- 
bata but is easily distinguished by the possession of two pairs of eyes, all about 
the same size. The life history of this tick is very similar to that of 0. moubata. 
The females oviposit after each blood meal, and the total number of eggs 
varies widely. CunlifTe (1922) reports a total of 400 under laboratory condi- 
tions. Under experimental conditions the life cycle from egg to adult varied 
from 60 to over 103 days. Its hosts are various domestic animals as horses, 
cattle, camels, dogs, pigs, goats, but it seems to prefer man (Bedford, 1934). 
Its distribution in Africa closely corresponds to that of 0. moubata, and in 
addition it is found in parts of Arabia and India. Senevet (1937) reports it 
from Tunisia, Algeria, and North Africa generally. It is known to be a vector 
of relapsing fever. 

Ornithodoros hermsi Wheeler, Herms, and Myer is a comparatively small 
tick (Fig. 14), not much more than half the size of O. turicata. It may be 
recognized by the size and the absence of dorsal humps on tarsus I. It has been 
taken only at high elevations (3000 to 9000 feet) in the mountainous regions 
of the western United States (California, Colorado, Oregon, Washington, 
Nevada, and Idaho). The tick is primarily a parasite of small mammals, as the 
western chipmunks, Eutamias spp., and probably other rodents. It has been 
taken in the nests of its hosts, and Davis (1939) reports taking many ticks 



THE ORDER ACARINA 



53 



in chipmunks' nests in old Douglas fir (Pseudotsuga taxijolia) stumps in east- 
ern Colorado at an elevation of 8800 feet. Wheeler (1943) gives a full account 
of the biology of this tick. The females deposit their eggs in batches, the maxi- 
mum number obtained being 232. The eggs hatch in 9 to 24 days (under 
constant temperature of 75 F. and 90 per cent humidity); there may be two 
larval stages and three or four nymphal stages. The normal time for develop- 
ment from the egg to the adult stage is about four and one-half months. 
The adults are apparently long-lived, as Wheeler kept some females for over 




Fig. 21. Distribution of argasid ticks in the United States. A. persicus, generally south 
of the line of dashes, and two isolated spots, one in British Columbia, and one in Balti- 
more, Md.; Ornithodoros turicata, generally south of line of dashes and north indicated 
by circles; 0. parfyeri, generally west of line of dots; O. hermsi, places collected indicated 
by X's; 0. corlaceus, indicated by stars. (After Cooley and others.) 

four years without any food, and others by occasional feedings for more than 
six and one-half years. This tick is known to be a vector of relapsing fever in 
many parts of its range. 

Ornithodoros turicata (Duges) is a large tick (Fig. 14) and is widely dis- 
tributed in the southwestern United States (Fig. 21), Florida, and parts of 
central Mexico. It is frequently found in great numbers in caves, in holes of 
burrowing animals, and in camps. Its hosts include nearly all our domestic 
animals, rodents, snakes, and terrapins as well as man. Hoffman (1930) reports 
them as abundant in pigsties in central Mexico. Under experimental condi- 
tions Francis (1938) reared the tick from egg to adult in nine months and 



54 MEDICAL ENTOMOLOGY 

ten days. He found four nymphal stages, though five nymphal stages were 
observed in four females and only three nymphal stages in one male. The 
species is an excellent vector of relapsing fever, and Davis (1943) has dem- 
onstrated transovarial transmission to the fifth generation, securing a 100 
per cent infection with the fifth generation. He concludes that this tick may 
be a more efficient "spirochactal reservoir" than the rodent hosts. Francis 
(1938) obtained transmission of relapsing fever in infected ticks after four 
years of starvation; two and a half years later he demonstrated the presence 
of the spirochetes in ticks that had only one feeding during that period (six 
and a half years). 

Ornithodoros parpen Cooley (Fig. 14) is very similar to O. turicata but 
may be recognized by the much smaller mammillae. It has been taken in 
widely separated areas in nine western states from Washington south to 
southern California and east to Colorado (Fig. 21). Jellison (1940) took large 
numbers in the nests of the burrowing owl, Speotyto cunicularia, and found 
the larvae of this tick engorged. Its principal hosts are recorded as Citellus spp., 
Cynotnys spp., Marmota sp., Peromysctts sp.,'Lepus sp., Sylvilagus sp., Mustela 
sp., and man (Cooley, 1944). Davis (1941) reared large numbers of this tick 
and records two nymphal stages for some males and three to four nymphal 
stages for females and males. The average developmental time from larval 
feeding varied from about 53 days to over 250 days. This tick is an efficient 
vector of relapsing fever, and Davis (1943) has shown experimentally that it 
can transmit, in all stages, the spotted fevers of the United States, Colombia, 
and Brazil with equal facility even to the second and fourth generation 
through the egg. He suggests that this tick may serve as a "spotted fever 
reservoir" in nature and may occasionally infect man. The tick is apparently 
long-lived as Davis has kept nymphs and adults for four years without feeding. 

Ornithodoros talaje (Gucrin-Men.) occurs from California and Kansas 
south to Argentina. In the tropics and subtropics of the Americas it is cosmo- 
politan and is frequently present in large numbers. In the United States it 
is recorded from California, Nevada, Arizona, Kansas, Texas, and Florida. 
This tick (Fig. 14) has been confused with O. rudis Karsch and O. kellyi 
Cooley and Kohls, and it is difficult to interpret the published accounts. Its 
hosts are known to be various mammals, birds, and reptiles. The larval stage 
is most common on rats in Panama, and in the United States this tick has been 
taken in association with rodents. Dunn (1931, 1933) reports it in houses 
attacking man, and the later stages were found in beds and other parts of the 
homes. The larva of this species requires a long time to feed (several days) 
and then leaves the host and molts twice before feeding again. There are three 



THE ORDER ACARINA 55 

to four nymphal stages, but the nymphs require only a few hours to feed. 
Under laboratory conditions Davis (1942) has reared this species in eight 
months. The principal hosts of the larvae are various species of rats, though 
Dunn has taken them on chickens, opossums, monkeys, cats, and dogs in 
Panama. This tick is known to be a transmitter of relapsing fever in Panama, 
Colombia, and Guatemala; relapsing fever spirochetes have been recovered 
from ticks captured in Arizona and Texas. 

Ornithodoros \dleyi Cooley and Kohls is noted here because it has been 
confused with O. talaje. As far as known, this is a parasite of bats, and it has 
been reported under the name talaje from houses in New York, Wisconsin, 
and Minnesota (Matheson, 1931 ; Herrick, 1935; and Riley, 1935). It apparently 
occurs in places where bats live or roost. It also has been reported from houses 
in Illinois, Iowa, and Pennsylvania (Cooley, 1944). In one house in New York 
it has been present since 1925, the last tick being found about December 13, 
1940. 

Ornithodoros rudis Karsch (O. vcncziielcnsis Brumpt; 0. migonei Brumpt) 
is closely allied to O. talaje, and these two species have been confused in litera- 
ture. However, man is the only known host of O. nidis, which is a house 
dweller, often occurring in large numbers in primitive dwellings where it 
hides during the day in cracks, crevices, holes, bedding, and similar places. It 
is a night feeder. The larvae feed rapidly and molt after feeding; there are two 
to four nymphal molts. Under experimental conditions the life cycle from 
egg to adult may occupy only three months (Davis, 1942). Its known dis- 
tribution is Panama, Colombia, Venezuela, and Paraguay. It is the important 
transmitter of relapsing fever in Panama, Colombia, and Venezuela. Davis 
(1943) has shown that the causative agents of the spotted fevers of Colombia, 
of Brazil, and of the United States can be conserved in the tissues of this tick 
for 343 days, 191 days, and 243 days, respectively; furthermore, the Colombian 
spotted-fever agent was transmitted through the egg to the next generation. 
Davis did not get transmission by the bites of this tick. 

Ornithodoros coriaceus Koch, the pjaroello, is a large tick and is much feared 
on account of its bite. It occurs in many parts of California extending from 
near San Francisco south along the coast (Fig. 21) in the more mountainous 
regions into Mexico, where Hoffman (1930) records it as native to the hot and 
temperate regions along the Pacific coast to Chiapas. Herms (1939) found it 
commonly in deer beds among the low scrub oaks. It is a parasite of large 
mammals and bites man freely. Herms (1916) gives its life history, under ex- 
perimental conditions, as requiring about 15 months from egg to egg. He also 
reared mature males in about four months. The larvae require several days (8 



56 MEDICAL ENTOMOLOGY 

or more) to engorge, and then undergo two molts before feeding again. 
There are three to six nymphal stages. The nymphs and adults feed very 
rapidly, becoming engorged in 10 to 40 minutes. The females lay several 
batches of eggs and may live for several years. The bite of this tick is very 
severe. It is not known to transmit any disease. 

A goodly number of other species of Ornithodoros have been recorded as 
biting man and some of them as playing a part in the transmission of disease. 
O. brasiliensis Aragao is reported from Brazil and bites man but is not known 
to transmit disease. O. rostratus Aragao occurs in Argentina, Paraguay, Brazil, 
and Bolivia. It is said to occur in houses and its bite is severe. 0. nicollei 
Mooser was described from Mexico, where it occurs in native huts; Davis 
(1943) gives its life history, reports it readily infected with the rickettsiae 
of the spotted fevers of the United States, Colombia, and Brazil, and has 
proved transovarial transmission. The tick has been taken from dogs, species 
of Neotoma, man, and a rattlesnake. O. delanoei Roubaud and Colas-Belcour 
was described from porcupine burrows in Morocco. It is a large species, the 
female being 18 mm. in length. The same authors (1936) give an account of 
its life history, concluding that it requires about five or six years from egg to 
maturity (under experimental conditions). O. erraticus (Lucas) [0. maro- 
canus Velu] occurs throughout the western littoral of the Mediterranean and 
south to Senegal. Brumpt (1936) records this tick as infected with Spirochaeta 
duttoni at Dakar; it is a vector of relapsing fever in Spain and parts of North 
Africa. It is found commonly in pigsties and burrows of various animals such 
as porcupines, jackals, and rats. O. jolcyi Parrot was described from Algeria 
and reported as feeding on man. O. tholozani (Laboulbene and Megnin) 
[= O. papillipes Birula] is reported from the Caucasus, Turkestan, Iran, 
Syria, Palestine, and the island of Cyprus. It is known to transmit relapsing 
fever in Russia and Cyprus. Russian workers report it as living at least 25 
years. Its hosts are camels, chickens, porcupines, jerboas, and various rodents. 
It readily feeds on man and is found in human dwellings. 0. lahorensis Neum. 
is widely distributed in Russian Turkestan, Iran, Transcaucasia, Tibet, Pales- 
tine, Asia Minor, and Cyrenaica; it is also found in India (the Punjab). It 
is not known to transmit relapsing fever but transmits anaplasmosis of sheep. 
Its bite is severe and is recorded as killing sheep. 0. normandi Larrousse is 
reported as abundant near El Kef, Tunisia; it bites man readily. 

THE GENUS OTOBIUS: This genus has, at present, only two well- 
defined species. O. megnini (Duges), more generally known as Ornithodoros 
megnini, is the spinose ear tick. It lives in the ears of its hosts, which are mainly 
horses and cattle. It also attaches to the ears of mules, asses, sheep, goats, hogs, 



THE ORDER ACARINA 57 

dogs, cats, coyotes, deer, rabbits, and some other animals. It receives its name 
from the spiny last nymphal stage, which is the stage most commonly seen in 
the ears of its host. This stage leaves the host and molts on the ground into 
a smooth, typical tick; however, the large hypostome of the nymph is replaced 
by a vestigial one. The adult does not feed. The female lays her eggs on the 
ground, and the larvae on hatching are very active. Reaching the ears of their 
hosts, they attach deep down in the folds and become fully engorged in about 
a week. Then follows the larval molt; there is a second molt soon after, and 
this is the last nymphal stage, the spinose stage. The entire life cycle may be 
completed in a month and a half under favorable conditions, or it may be 
greatly prolonged. The adults may survive for a year or more. This tick was 
originally described from Mexico but has become widely distributed through- 
out many parts of the world. In North America it extends from British Colum- 
bia south and east to Kentucky and North Carolina. I have taken this species in 
the ears of cattle shipped from Texas to Ithaca, New York. The species is 
widespread in Mexico and parts of South America. Brumpt (1936) states that 
it is well established in the Transvaal and other parts of South Africa. Kingston 
(1936) reports it in the ear of a gelding that had been born and reared in 
Australia. This tick has been reported found several times in the ears of 
man. 

Recently Cooley and Kohls (1940) described another species, O. lagophilus, 
from rabbits. The species occurs in the northwestern United States and British 
Columbia. 

In addition to the species mentioned above many others are known. The 
genus Ornithodoros contains several species described from bats, bat roosts, 
or bat dung, as well as from other hosts. 

THE FAMILY IXODIDAE 

This family contains the vast majority of ticks distributed among some 10 
or 12 genera. Only a few of the more important species can be treated here. 

' THE GENUS BOOPHILUS: Boophilus annulatus (Say) (Figs. 22,23) 
the common cattle tick of North America and Mexico. In the United States 
it is normally restricted to south of 37 North latitude, and in this area the 
tick has been largely eliminated by dipping and other practices; where pres- 
ent it is under strict quarantine control. The tick is a one-host tick. The females 
deposit their eggs on the ground, each female laying from 3000 to over 5000 
eggs. The incubation period of the eggs depends largely on temperature and 
moisture and varies from 19 days (minimum) in summer to 180 or more 
days in late autumn, with varying periods between these extremes during the 



58 MEDICAL ENTOMOLOGY 

rest of the year (Graybill, 1941). The seed ticks are very active and climb up 
blades of grass and various objects to await a passing host. The larvae can 
survive long periods from a maximum of 85 days for eggs hatching in July 
to 234 days for eggs hatching in October. The developmental period on the 
host (larva, nymph, adult) varies from 20 to 65 days. Mating takes place on 
the host, and the female after engorging drops off; egg laying begins in from 
three days to as long as nearly 100 days (females dropping in November) . This^ 
tick is a very important species as it transmits the organism (Piroplasma 
bigemina) of the so-called Texas fever, red-water fever, or hemoglobinuria. 




Fig. 22. The cattle tick (Boophilus annulattis}. Male, ventral view. 
(After Salmon and Stiles.) 

This was demonstrated by Smith and Kilbournc (1893), and they showed 
that the organism develops in the red blood cells of cattle, destroying them. 
The tick in feeding obtains the infective stage of this parasite, which under- 
goes a developmental cycle (later elucidated by Dennis, 1932) and is passed 
on to the young of the tick through the egg (the so-called transovarial or 
hereditary transmission). It is of interest to note that this was the first tick that 
was shown to be an intermediate host of a protozoan parasite and the first case 
of proven transovarial transmission of any parasite. The principal hosts of this 
tick, besides cattle, are horses, mules, sheep, goats, and probably deer. 

A number of species or subspecies of this tick have been described from vari- 
ous parts of the world: Boophilus australis Fuller from Australia, the Philip- 



THE ORDER ACARINA 59 

pine Islands, the Dutch East Indies, India, and South America; B. microplus 
Canestrini from South America, Central America, West Indies, Mexico, 
Florida and probably other parts of the world; B. decolorutus Koch from 
South Africa. Minning (1934, 1936) has added a number of doubtful species. 

THE GENUS DERMACENTOR: This genus contains some very im- 
portant North American species. The principal characters that readily dis- 
tinguish this genus are as follows: ornate, with eyes and festoons (always ir) ; 
basis capitulum quadrangular in dorsal view; coxae I to IV gradually in- 
creasing in size, with coxa IV very large; coxa I always bifid; anal groove 
posterior; males without ventral shields. 

In North America Cooley (1938) describes seven species, and probably over 
twenty species are at present known from the world. No species are known 
from South America (Cooley, 1938). 

Dcrmacentor variabilis (Say), the dog tick (Fig. 9) or wood tick, is widely 
distributed in North America east of a line drawn from eastern Montana 
south to Texas; it also occurs in Canada east of Saskatchewan; another area 
is in California west of the Cascade and Sierra Nevada Mountains (Fig. 24). 
It is most abundant along the Atlantic seaboard from Massachusetts south to 
Florida and in certain inland areas such as southern Iowa and parts of Wis- 
consin and Minnesota (Bishopp and Smith, 1938). This is a three-host tick. 
The adults prefer large mammals such as dogs (the preferred host), cattle, 
horses, hogs, sheep, man, and a wide variety of wild animals. The adults 
require from 5 to 14 days to engorge. Mating takes place on the host. Dropping 
from the host the females lay their eggs in some secluded place on the ground; 
each female lays from 4000 to 6500 eggs. The eggs hatch in from 26 to 40 days 
(depending on the temperature), and the larvae can survive without food 
for at least n months. The principal larval hosts are mice (Peromyscus, Micro- 
tits, and Pity my s spp.), and the time of attachment varies from 2 to 14 days. 
The larvae then drop from their hosts and molt to the nymphal stage. Nymphs 
can survive at least six months without food. The nymphs attach to the same 
host as the larvae and engorge in from 3 to 10 days. Dropping from the hosts, 
the nymphs molt to the adult stage in from three weeks to a much longer 
period. The entire life cycle from egg to adult varies from 54 days to much 
longer, depending on the available food supply and the temperature. This 
tick is the important vector of Rocky Mountain spotted fever and tularemia 
in parts of its range, 

Dermacentor andersoni Stiles (yenustus Banks) is commonly caller) t^e 
"Rocky Mountain spotted-fever tick" (Figs. 4,5) as it was first shown to be the 
vector of a peculiar disease of man called "Rocky Mountain spotted fever." 



60 MEDICAL ENTOMOLOGY 

Its distribution is restricted to parts of the western United States and western 
Canada (Fig. 24). Its greatest abundance is in the northern part of the Rocky 
Mountain region of the United States, and there it is most common in areas 
"where the predominating vegetation is low, brushy and more or less open, 
i.e., in areas where there is good protection for the small mammalian hosts 
of the larvae and nymphs and sufficient forage to attract the large hosts, either 
wild or domestic, of the adult ticks. It is relatively quite scarce in heavily tim- 
bered areas or country of a strictly grassland, prairie type" (Parker et al. t 





Pig. 23 (lejt). The cattle tick (tioophilus annulatus). Fully gorged female. (After 
Salmon and Stiles.) 

Fig. 24 (right). General distribution of Dcnnaccntor variabilis (dotted area) and 
D. andcrsoni (lined area) in North America. 

1937). At present it is known from 14 western states Washington, Oregon, 
California, Nevada, Arizona (northern part), New Mexico (northern edge), 
Utah, Colorado, Idaho, Wyoming, Montana, and the western edge of North 
and South Dakota and Nebraska; it is also present in southern British Colum- 
bia (dry regions of the Kootenay district and north), southern Alberta, and 
southern Saskatchewan. The tick has been spreading, and it may eventually 
occupy a much wider range where suitable hosts and conditions exist. 
This tick is a three-host tick, and its life cycle is interesting and complicated. 



THE ORDER ACARINA 61 

The fertilized females drop from the larger hosts during April, May, and 
June or early July. They deposit their eggs in some protected place on the 
ground, each female laying from 2000 to 8000 eggs over a period of about a 
month. The eggs, depending on temperature and other factors, hatch in from 
one to two months. The larvae attach to some of the smaller mammals, 
particular rodents, as the ground squirrel (Citdlus columbianus) , pine squirrel 
(Sciurus hudsonicus richardsoni), chipmunks (Eutamias spp,), and most of 
the other native rodents as porcupines, prairie dogs, and various species of 
rabbits. As Cooley remarks, "Almost any mammal that is available is used." 
The larvae become engorged in two to eight days and drop from their hosts. 
Molting takes place on the ground, and the nymphs normally pass the winter 
unfed. During the following spring and summer the nymphs attach to the 
same type of hosts as those of the larvae. After engorgement the nymphs drop 
from their hosts, molt on the ground, and pass the second winter as unfed 
adults. The following season the adults attach to the larger mammals, pre* 
ferring horses, cattle, sheep, bears, coyotes, mountain goats, deer, man, and 
also the jack rabbits, snowshoe rabbits, and porcupines, but usually riot any of 
the smaller rodents. The presence of the larger mammals seems essential for the 
maintenance of this tick in abundance. They attach from March to July each 
year and mate on the hosts. The complete cycle from egg to egg thus requires 
two years, though there are many variations due to the failure to find suitable 
hosts, climatic factors, and other "conditions. The most striking features of 
the life cycle are its length, two years, and the change of hosts from small 
rodents, as larvae and nymphs to the larger mammals as adults. This tick is 
a very important vector of Rocky Mountain spotted fever, tularemia, "Q" 
fever, and Colorado tick fever; it is the cause of tick paralysis. 

Dermacentor occidentalis Marx can be recognized by the long cornua and, 
at present, its restricted distribution. It is known only from the Pacific coast 
along the Coastal Ranges 'and Cascade Range from northern Oregon to 
southern California. Cooley (1938) reports it as very abundant in southern 
Oregon. This is a three-host tick. The adults attach to cattle, horses, deer, dogs. 
mules, asses, and man. The larvae and nymphs attach mostly to the smaller 
rodents, such as ground squirrels, wood rats, chipmunks, and rabbits, and 
occasionally to larger animals. The larvae, nymphs and adults engorge on 
their hosts in three to six or more days, and the entire life cycle may be com- 
pleted in less than three months. In nature this tick may be found at all 
seasons. It is a serious pest of cattle. It also readily attaches to man qnrl its 
bite is severe. At present it is known to transmit tularemia and it is strongly 



62 MEDICAL ENTOMOLOGY 

juspected of transmitting Rocky Mountain spotted fever. Experimentally it 
can transmit spotted fever in all stages, from stage to stage, and through the 
egg to the larvae. 

Dermacentor parumapertus Nctim. is primarily a rabbit tick, as rabbits (all 
species) are the hosts of all stages. It is rarely found on other hosts. The 
species occurs in the southwestern United States, from Oregon, southern 
Idaho, and southern Wyoming south to Mexico and east to Kansas and central 
Texas. Parker et al. (1937) have shown stage-to-stage survival of Rocky Moun- 
tain spotted fever in this tick, and it seems probable that the tick may serve as 
an agent in maintaining the virus in nature in rabbits. 

Dermacentor albipictus (Pack.), the moose or elk tick, is markedly different 
from all other species of Dermacentor as it is a one-host tick. Its hosts are the 
larger domestic and game animals, such as cattle, horses, elk, moose, and deer. 
The ticks are present on their hosts only during the winter season, from Sep- 
tember (usually) to early spring. The females lay their eggs on the ground, 
and when they hatch the larvae bunch together and are torpid during the 
warmer months; they become active at the approach of cold weather and 
seek out their hosts. Once attached, the tick completes its life cycle, only 
dropping when the adult stage is reached. This tick is widely distributed 
throughout North America and is frequently a serious pest of elk, moose, deer, 
and horses in its northern range in Canada. Thomas and Cahn (1932) report 
this tick to be a vector of a serious disease of moose in northern Minnesota and 
adjacent regions of Ontario. 

THE GENUS IXODES: The species of this genus can be recognized readily 
by the anal groove curving around the anus in front. They are inornate, with- 
out eyes, and lack festoons. Males differ from females: they have ventral 
plates, i median, i anal, and 2 adanals (a pregenital and 2 epimeral plates may 
also be present) ; they are normally much smaller than the females. Over one 
hundred species have been described, but probably not over fifty can be con- 
sidered good species. Comparatively little is known about their biology, dis- 
tribution, bionomics, or hosts; a few species have been thoroughly studied. 

Ixodcs ricinus (Linn.) 2 is probably world-wide in distribution. Its hosts 
include cattle, dogs, horses, cats, deer, foxes, sheep, man, and other animals. 
It is a thrpe-hp.<ff fink. As it is the vector of louping ill of sheep in Great Britain 
(northern England and Scotland) it has been studied intensely in recent years. 
The tick appears to require a moist climate (70 to 80 per cent relative humid- 
ity) for its best development. MacLeod (1932-1936) reports the female lays 
2400 to 3200 eggs; the eggs hatch in 4 to 10 weeks; the larval and nymphal 

2 Cooley (1945) does not consider that this tick occurs in North America. 



THE ORDER ACARINA 63 

stages are usually completed in from 16 to 20 weeks. He found the males and 
females can live nearly two years, the larvae two years, and the nymphs over 
a year, without feeding. The rapidity of development depends on the various 
stages finding available hosts. It is probable that it normally requires almost 
a year for the complete life cycle. Recently this tick has been found to transmit 
louping ill of sheep in the U.S.S.R. (Silber and Shubladze, 1945). Louping 
ill has also been reported from man. This tick is also the most important 
vector of piroplasmosis (Babesia bovis) of cattle in Europe. 

Ixodes pacificus Cooley and Kohls (usually called calijornicus Banks) 
closely resembles Ixodes ricinus. It occurs commonly along the Pacific coast 
from southern British Columbia to Mexico west of the Cascade Mountains. 
The adults attack a wide range of animals including man. The immature 
stages also attach to cold-blooded animals and birds. As it is a three-host tick, 
it may prove of some importance in the transmission of disease. 

Ixodes cooled Pack, is a common tick in the eastern United States and 
occurs on a variety of animals such as woodchucks, foxes, squirrels, skunks, 
weasels, dogs, and cows. It is not an uncommon tick on humans. The author 
has nine records from humans: two ticks taken from the eyelids of children, 
two from the shoulders of adults, four from the head and neck, and one from 
below the breast all were from the central New York region. This tick has 
not been studied to determine whether it can transmit any disease. Ixodes 
holocyclus Neum. occurs in India, Australia, and the East Indies. Its life cycle 
is quite similar to that of 7. ricinus. It has a wide range of hpsts, including man. 
7. pilosus is widespread in South and East Africa. The last two species are 
notorious for the production of "tick paralysis" in man and animals. 

THE GENUS AMBLYOMMA: This is a large genus of ornate ticks; they 
abound principally in the tropical and subtropical regions. They may be recog- 
nized by the long palpi and hypostome; the second segment of the palpus is 
over twice as long as it is wide, and the hypostome is armed with teeth only on 
the apical half. Eyes and festoons are present. Although over ninety species 
have been described, Cooley (1944) lists only seven species from North Amer- 
ica. The species are most abundant in South America and Africa and are very 
difficult to diagnose. 

Amblyomma americanum (Linn.), the lone-star tick (Fig. 25), is easily 
identified by the solitary white spot on the posterior margin of the scutum of 
the female. It is widely distributed in the United States east of central Texas 
north to southern Iowa and east to the Atlantic seaboard. It is recorded as 
abundant in the Ozark region and occurs commonly along the south Atlantic 
coast and in the canebrakes of Louisiana and Mississippi as well as in wooded 



64 MEDICAL EJ-ITOMOLOGY 

regions of many of the southern states. It is a three-host tick, and in its 
southern range it breeds throughout the year. The larvae and nymphs occur 
on a wide range of hosts including birds; all stages attack many different mam- 
mals such as cattle, horses, hogs, and man. Its bite is very painful and may 
be followed by suppurating sores. The larvae, nymphs, and adults can survive 
nearly a year or longer without food. This tick is a vector of Rocky Mountain 
spotted fever (Texas and Oklahoma), is a suspected vector of "Q" fever and 
tularemia, and is reported as a transmitter of a new clinical syndrome, 
"Bullis" fever. 




Fig. 25. Left: Amblyomma cajennense. Right: A. americanum. Adult females. 

Amblyomma cajennense (Fabr.) is distributed from the southern tip of 
Texas south through Central America, Panama and south along the Atlantic 
seaboard to Argentina. Unlike the lone-star tick the scutum has an extensive 
pale pattern (Fig. 25), and the internal spur of coxa I is about one-half as 
long as the external spur. It is a three-host tick and all stages readily attach to 
man. Where it occurs in abundance, it is very annoying to all domestic animals 
and many wild animals, and man suffers very severely from its attacks. As the 
tick is very small (3 to 3.5 mm. in length in the female), it easily gains access 
through clothing. The bites are very deep owing to the long mouth parts and 
frequently develop into sores that are difficult to heal. In Brazil and Colombia 
it is the recognized vector of spotted fevers (Brazilian spotted fever and Tobia 
fever). These diseases are presumably identical with Rocky Mountain spotted 
fever, and A. cajennense may prove a suitable vector when this disease is intro- 
duced into southern Texas. 

Amblyomma maculatum Koch is an important pest of livestock along the 
Atlantic and the Gulf coasts, extending from South Carolina west to Texas. It 
also occurs throughout South and Central America. The larval and nymphal 



THE ORDER ACARINA 65 

stages attach to birds and some of the smaller wild mammals; the adults attach 
in the ears and when abundant produce inflammation and swelling. The 
points of attack furnish ideal places for infestation with screw worms, which 
may result in the death of the animals. 

Amblyomma hebraeum Koch, the bont tick, is widespread in South Africa. 
It is a three-host tick and, in all stages, attaches to man as well as to many 
domestic and game animals. In its range it is a vector of tick-bite fever of man 
and heart water of cattle, sheep, and goats. Many other species of Amblyomma 
occur in Africa and are important pests of domestic and game animals, and 
some are vectors of serious diseases. 

THE GENUS RHIPICEPHALUS: The ticks of this genus are practically 
always inornate, with eyes on the margins of the scutum and with festoons. 
When viewed dorsally the capitulum is generally hexagonal in outline. The 
males are smaller than the females and possess ventral shields. Over thirty 
species are recognized, and of these more than twenty are known from Africa. 
In North America there is one species, which is world-wide in distribution. 

Rhipicephalus sanguineus (Latr.), the brown dog tick (Fig. 9), is widely 
distributed in the United States and occurs in most of the temperate and 
tropical regions of the world. It was first reported from southern Texas in 1912, 
and since then it has spread to most parts of the continent. It is primarily a 
pest of dogs and has not been reported as a pest of man in the United States. 
In the temperate climates this tick seeks warm places such as houses, dog 
kennels, and similar places where it may pass generation after generation. 
In warmer climates it occurs out of doors, often in great numbers. It is a three- 
host tick and all stages develop readily on dogs. Under favorable conditions 
the entire life cycle from the egg to the adult may be completed in less than 
two months. In the North this tick often becomes very abundant in private 
homes where dogs are allowed to wander at will. They may be found in 
cracks and on the walls, floors, and ceilings. They are difficult to eradicate. 
In some parts of the world, as about the Mediterranean region and in Africa, 
this tick is known to attach to man. It is also reported attacking man in 
Mexico. It is a vector of several diseases. It is known to transmit boutonneuse 
fever and Kenya tick typhus and has been shown experimentally to be capable 
of transmitting Rocky Mountain spotted fever and Spanish relapsing fever; 
it is also implicated in tick-bite fever and "Q" fever. Bustamente et al. (1946) 
have found this tick naturally infected with Rocky Mountain spotted fever 
in Mexico. It is an important vector of canine piroplasmosis (Babesia canis) 
or malignant jaundice of dogs; this disease is common in the Mediterranean 
region and South Africa and has recently been reported from Florida. 



66 MEDICAL ENTOMOLOGY 

Other species of this genus are important vectors of serious diseases of 
domestic animals in various parts of Africa. R. appendiculatus, R+ capensis, 
R. evertsi, and R. simus are vectors of East Coast fever of cattle; the last two 
are also involved in the transmission of red-water fever of cattle; R. simus, 
R. sanguincus, and R. bursa are vectors of bovine anaplasmosis (Anaplasma 
marginale) ; and other species are known to transmit several different diseases. 

THE GENUS HAEMAPHYSALIS: The ticks of this genus are small, 
eyeless, and inornate but with festoons. The second segment of the palpus 
projects laterally at its base and gives the capitulum a triangular appearance 
in dorsal view. More than fifty species have been described, but only a few 
of them are known to play any part in disease transmission. 

Haemaphysalis leporis-palustris (Pack.), the rabbit tick (Fig. 9), plays an 
intermediate but important part in the transmission of Rocky Mountain 
spotted fever and tularemia. According to Green and his associates (1943), 
the favorite host of this tick in all stages is the snovvshoe hare, the second most 
important host is the ruffed grouse, and the cottontail rabbit is the third. In 
addition, this tick is reported from more than sixty species of ground-loving 
birds, from many different rodents, and occasionally from domestic animals. 
The larvae and nymphs are the stages most commonly found on birds. It 
is not known to attach to man; only one case has been reported by Brown 
(1946) in Alberta, Canada. The tick is a three-host tick and feeds, in the 
North, during the spring, summer, and autumn. It hibernates in all stages on 
the ground. In the South the tick is found on its hosts throughout the year. The 
life cycle may be completed in as short a time as 75 clays, or it may be greatly 
prolonged if hosts and conditions are not favorable. All stages of the tick are 
capable of surviving long periods of starvation. The importance of this tick 
lies in its ability to transmit Rocky Mountain spotted fever and tularemia 
among the reservoir hosts. If infected the tick can transmit these diseases to 
susceptible hosts at each feeding. The rabbit tick is widely distributed from 
Alaska and Canada throughout the United States and Central and South 
America to Argentina. 

Haemaphysalis leachi (Aud.) is an important tick with a wide distribution 
in Africa, Asia, and throughout the Australasian region. It is the vector of 
canine piroplasmosis (Babesia canis) and is reported as a transmitter of tick- 
bite fever in South Africa. PL humerosa of Australia has been shown to 
transmit "Q" fever among bandicoot rats, a natural reservoir of the disease, 
while H. bispinosa is thought to be one of the vectors to man. Other ticks are 
recorded as playing a role in the transmission and maintenance of this disease 
in Australia. 



THE ORDER ACARINA 67 

4 TICKS AND DISEASE 

Our knowledge o ticks and the role they play in the causation of diseased 
conditions in man and other animals and in the transmission of pathogenic 
organisms has greatly increased during the past few years. Smith and Kil- 
bourne (1893) were the first to prove that the ordinary cattle tick, Boophilus 
annulatus (Say), is the vector of Texas fever, red-water fever, or hemo- 
globinuria of cattle. Furthermore they showed that the organism Piroplasma 
bigemina is passed through the egg to the larva. Infection occurs when larvae 
descended from infected mothers feed on nonimmune cattle. This was the 
first demonstration of the passage of a pathogenic protozoan from the parent 
to the offspring. During the intervening years a large number of ticks have 
been shown to be the vectors of many serious diseases of man and other ani- 
mals. At present the interrelations of ticks and disease may be roughly classi- 
fied as follows: 

1. Direct effects produced by their bites. 

2. Causation of paralysis, known as "tick paralysis." 

3. Hosts and vectors of pathogenic organisms. 

TICK BITES 

Tick bites arc at times rather serious. In many domestic and game animals 
the loss of blood is often great; frequently the mass attack, especially in young 
animals, results in death or weakness, which exposes them to disease or 
destruction by their enemies. Moose and elk have frequently been reported 
as weak and dying from mass attacks of Dermacentor albipictus, and young 
cattle are undoubtedly killed by attacks of Boophilus annulatus. When ticks 
bite there is injected into the wound the secretions of the salivary glands, which 
in some cases are known to possess an anticoagulin and in others a toxin. 
Whatever may be present, the bites of certain species produce ugly ulccrations, 
which are difficult to heal and which offer ideal conditions for the invasion 
of pathogenic organisms or the attacks of myiasis-producing flies. Widely 
varying effects are reported by different workers. This should be expected since 
insect bites affect different people in the most varied ways. When a tick has 
buried its capitulum deeply, it should be removed with great care. Holding 
the lightened end of a cigarette to the tick will usually cause it to loosen its 
hold. It should then be carefully removed and not crushed by hand but stamped 
on or placed in alcohol. Crushing it might result in infection if the tick hap- 
pened to be carrying some pathogenic organisms. Another method o tick 
removal (said to be effective by those using it) is to place a piece of adhesive 



68 MEDICAL ENTOMOLOGY 

tape over the tick, attaching it firmly on both sides of the tick. This will cause 
the tick to withdraw its mouth parts and it then can be removed without 
tearing the flesh. The wound should be treated by some antiseptic such as 
alcohol, and, if a physician is available, he should be consulted. Should infec- 
tion result the physician will have a better chance to give the correct treatment. 
Table 3 lists ticks that are recorded as producing severe wounds on man by 
their bites. The bites of many other ticks are annoying, but little information 
can be found about them. 

Table 3. Ticks whose bites may have severe effects on man. 



Species 


Effect of bite 


Authority 


Argas mianensis 


Severe; produces fever 


Nuttall and others 


A. brumpti 


Bite severe and wound 
pruriginous for long time. 
After 25 years nodules 
still persist at location 
of bite 


Brumpt (1927) 


Ornithodoros 


Extensive ecchymosis 


Patton (1913) 


savignyi 






O. gurneyi (Australia) 
on Kangaroo 


Reported to cause paralysis, 
blindness, and unconscious- 


Man. Trop. Mcd. (1945) 




ness 




O. turicata 


Effects severe 


Nuttall (1908) and others 


O. ro stratus 


Bites severe 


Davis (1945) 


O. talaje 


Effects severe 


Nuttall and others 


O. moubata 


Bites of nymphs, severe? 


Nuttall (1908) 


O. lahorensis 


Bites severe 


Vogel (1927) 


O. brasilienscs 


Bites severe 


Davis in Man. Trop. Med. 


I x odes ricinus 


Bites often accompanied 
by paralysis 


Nuttall (1908) 


I. ricinus (?) 


Severe, followed often by 
ulceration or glandular 
involvement 


Mail and Gregson (1938) 


/. pacificus (calijornicus) 


Bite severe and reactions 
often follow 


Various authors 


Amblyomma cajennense 


Severe, often followed by 
sores difficult to heal 


Various authors 



TICK PARALYSIS 



Tick^aralysis is a peculiar disease found mostly in young childrea~and.. 
domestic animals, such as sheep, dogs, cattle, and goats, when attacked^ by 



THE ORDER ACARINA 69 

certain sgecies of ticks. Thej)aralysisis_iisually .preceded by muscular weak- 
ness andjnability J:o co-ordinate the movements oj^thelegs, followed in a few 
hours by_ji more or less complete flaccid paralysis of the lower limbs. The 
paralysis extends rapidly _upjward, involving the arms and neck; speech and 
deglutition become.. difficulty and, if trie tick is not found and removed, death 
results from respiratory paralysis.. In many cases a marked rise in temperature 
occurs. In North America the. ticks involved are Dermacentor andersoni and 
D. variabilis; there is also a possibility that a species of Ixodes may play a part 
in British Columbia. When these ticks attach at the base of the skull, on the 
head, or along the spine, paralysis may result. If the tick or ticks are removed 
before paralysis reaches the respiratory state, recovery is usually prompt and 
rapid. Todd (1914) reviews the history of tick paralysis in British Columbia. 
For a long time practicing physicians in British Columbia have known this 
disease was associated with tick bites. Todd (1914) gives the records of ten 
cases reported by different physicians, and all except one recovered promptly 
after the removal of a tick (Dermacentor andersoni). He also gives details of a 
series of experiments with this tick; he obtained paralysis in a puppy and 
lambs but failed with monkeys and guinea pigs. Had wen (1913) and Nuttall 
(1914) confirmed these results by producing paralysis in sheep and dogs by 
the bites of D. andersoni. McCormack (1921) records 13 cases of tick paralysis 
in young children and one of a girl 21 years old. All recovered when the ticks 
were discovered and removed except in one case in which the tick was not 
noted till after death. Nuttall (1914) lists 13 cases as observed by Dr. Temple 
in Oregon. Cogswell (1923) lists 6 cases in children in 'Montana. Mail and 
Gregson (1938) report 26 cases from British Columbia during the period 
from 1910 to 1931; of these four died. Dermacentor andersoni was the tick 
involved. They also state that they have records of at least 150 cases from the 
province. Robinson and Carroll (1938) report a single case of tick paralysis 
in a young girl from Georgia caused by the bite of Dermacentor variabilis. 
Recovery was rapid when they found and removed two ticks from the parietal 
region of the skull. Gibbes (1938) lists a case of a young woman in South 
Carolina who was suffering from a peculiar paralysis when she was admitted 
to a hospital. The accidental finding and removal of a tick from the back 
of the scalp brought almost immediate recovery. The tick was undoubtedly 
Dermacentor variabilis. Undoubtedly physicians have treated many other cases 
of which we have no record. Ticks do not, in all cases, produce paralysis 
when they attach to young ^children^but, when children 



^ 

QCSS accompanied j^njibUityj^Q the legs, searcri 

should be made at ..once for ticks and they should be carefully removedT 



70 MEDICAL ENTOMOLOGY 

Tick paralysis also occurs among sheep. Hadwen (1913) reports many 
cases among lambs in British Columbia. Hearle (1933) reports an outbreak of 
paralysis among steers in British Columbia. Out of 900 steers 100 became 
paralyzed and 65 died. Moillett (1937) records 200 steers stricken in a herd of 
638 in the same province; of these 26 died. In all cases D. andersoni was the 
tick involved. In Australia paralysis in lambs, dogs, and children is caused 
by Ixodes holocydus Neum. Ferguson (1924) reports eight deaths of children 
in Australia from tick paralysis, all caused, he believes, from the bites of 
Ixodes holocydus. Ross (1926) records numerous experiments with this tick 
on dogs but was unable to determine the exact agent producing paralysis and 
death. Tick paralysis has also been reported from South Africa caused by the 
bites of Ixodes pilosus Koch. Veneroni (1928) reports two cases of tick 
paralysis in Italian Somaliland from bites on the neck by the tick Rhipi- 
cephalus simus Koch. In Europe Ixodes ricinus (Linn.) is known to cause 
a paralysis by its bites. 

This peculiar ascending motor paralysis has been reported from widely 
separated regions of the world and is caused by at least six different species 
of ticks. As the onset of the disease may easily be mistaken for poliomyelitis, 
it is essential that in all cases of paralysis of children search should be made 
for the presence of ticks. As a prophylactic measure all people, especially chil- 
dren, that camp, play, or live in tick-infested regions should be carefully 
examined each day for ticks. The head should be combed with care since the 
small unengorged ticks are not easily located. If ticks are found, report to a 
physician so that any sign of sickness may be treated at once. In all cases re- 
move the ticks so that the head is not left buried in the wound. If the head 
is left, have a physician remove it. 

TICKS AS VECTORS AND HOSTS OF PATHOGENIC ORGANISMS 
AND VIRUSES 

Human Diseases 

During the past fifty years ticks have been discovered to be the active 
vectors and hosts of many animal and human diseases. Smith and Kilbourne 
(1893) first demonstrated the relation of Boophilus annulatus (Say) and 
hemoglobinuria or red-water fever of cattle. The causative agent of this dis- 
ease is a minute protozoan, Piroplasma bigemina, which lives within and de- 
stroys the red corpuscles. It is a very serious disease, and no adequate treat- 
ment is known except the control of the ticks. A similar disease of cattle in 
Europe, caused by Babcsia bovis, is transmitted by the ticks Ixodes ricinus, 



THE ORDER ACARINA 71 

/. hexagonus, and probably other species. Numerous otber diseases of animals 
are transmitted by ticks, but space does not permit of more than a mention 
here. 

RELAPSING JFEVERS ; OF MAN (Tick-borne) : In recent years a large 
number of relapsing fevers, caused by Spirochacta spp. (often referred to 
under the generic names Spirillum, Treponema, or Borrelia) have been recog- 
nized by different workers. These relapsing fevers are characterized by re- 
peated attacks of fever, the attacks tasting from Tnree to five days. The periods 
of apyrexia vary from five to ten days. The causative agents of these fevers 
are species of Spirochaeta that are present in the blood, cerebrospinal fluid, 
and other body fluids and are most abundant during attacks of fever. During 
the apyrexial periods they may apparently be absent from the blgod^^trearn 
though experimental infection work has demonstrated their presence. The 
vectors of the various species of Spirochacta are^ticks and lice, though other 
arthropods. inay-at^tijiies_play.A.pait.. The presence of thejjpirochetes in the 
blood stream during* the entire infection period is of great significance 4 espe- 
cially when prophylactic measures are considered. Spjirgchsta..jrjeff.Htrsntif 
(Lebert), often referred to as S. obermeieri, was the first jsjjgcics. observed to 
infest the blood of man. It was first seen by Obermeier in 1868 and was de- 
scribed and named by Lebert in 1874. Ross and Milne (1904) were the first to 
demonstrate that a peculiar fever of West Africa was caused by a spirochete 
(now known as Spirochaeta duttoni) and that the spirochete was transmitted 
to man by a tick, Qrnithodoros moubata (Murray). Later, but independently, 
Dutton and Todd (1905) demonstrated that Q. moubata was the vector of this 
spirochete. Furthermore they proved that the newly hatched offspring of iat 
fected ticks were capjible of transmitting the disease. Since then it has been 
shown that infection in the tick can pass through the eggs even to the third 
generation. At present numerous species of spirochetes have .been described 
from the blood of man and animals. More than 12 species have been described 
as occurring In man, but there Js no general agreement that these are all dis- 
tinct species. Some authorities consider them to be nothing more than strains 
of the one species, S. recurrentis. 

Tick relapsing fevers are widely distributed throughout the world, being 
recorded from Europe, Asia, Africa,^orth, South, and Central , A_miiea^and 
Mexico. In NortrT America tick relapsing fever is known from at least 13 
western states and the southern part of British Columbia. Though relapsing 
fever was first recognized by Meader (1915) in Colorado and other physicians 
in California (1922) and Texas (1927), it was not till 1930 that Weller and 
Graham showed it to be tick-borne. They demonstrated that Ornithodoros 



72 MEDICAL ENTOMOLOGY 

turicata was the vector. Since then at least two other species of Ornithodoros 
have been recognized as active vectors in the United States. In practically all 
cases the spirochetes are passed from generation to generation through the 
eggs, and Davis is of the opinion that the active reservoirs of the spirochetes 
are the ticks rather than the susceptible animals such as rodents on which so 
many of the ticks feed. Table 4 will give in brief form the known tick vectors 
and the present distribution of the disease. The distribution of the ticks is 
usually much more extensive than that of the disease. Undoubtedly other 
species are involved, but data on them are not available. 

Table 4. Tick relapsing fever. 



Vector 


Distribution of ticks 


Known occurrence of disease 
(and name of spirochete strain) 


Ornithodoros 


Southwestern U.S.A., 


New Mex., Kansas, Okla., 


turicata 


Florida, and Mexico 


Texas, Mexico (S. turicatae) 


0, hermsi 


Calif., Col., Ore., 


Calif., Col., Idaho, Nev., Wash., 




Wash., Nev., Idaho 


British Columbia (?) (S. hermsi) 




(At high elevations, 






3000 ft.-f-) 




O. parfcri 


Nine western states 


California. (Ticks with spirochetes 




from Wash, to southern 


also taken in Idaho, Mont., Nev., 




Calif, and east to 


Wyo., and Utah) 




Mont, and Col. 


(S. par^eri) 


O. talaje 


Calif, to Kansas, 


Panama, Colombia, and Guatemala 




south to Argentina 


(S. venezuelensis) 


O. rudis 


Panama, Colombia, 


Panama, Colombia, Venezuela 


(venezuelensis) 


Venezuela, Paraguay 


(S. vcnezuclcnsis) 




(A house tick) 




0. moubata 


Africa from Lake Chad 


Throughout the range of the tick 




east to Red Sea and 


(S. duttoni) 




south to Cape Province 




0. savignyi 


Same area as O. moubata, 


Probably throughout its range 




also North Africa, 


(S. duttoni?) 




Arabia, and India 




O. erraticus 


Western littoral of 


Southern Spain and parts of Africa 




Mediterranean, Spain 


(5. hispanicum) 




south to Senegal in 






Africa 




O. tholozani 


Caucasus, Iran, Syria, 


Cyprus, parts of Russia (S. sp.?) 


(papittipes) 


Palestine, Cyprus 




0. nereensis 


Turkmenia (Russia) 


Turkmenia (Russia) (S. sp.?) 



THE ORDER ACARTNA 73 

The method q_transrnission o the spirochejgs, by.. the various specie^, of. 
ticks is not known in all cases. The ticks obtain the spirochetes when feeding 
on the blood of animals that are infected. In the tick the spirochetes multiply 
by transverse fission. The spirochetes invade the tissues and body cavity of the 
tick. When an infected tick bites a new host, the spirochetes gain entrance 
either through the coxal fluid glands, which eject their secretion (as in 0. 
moubata) or by way of the bite as in 0. turicata, 0. parpen, 0. hermsi, 0. 
tholozani, and probably others (Davis, 1945). 

, ROCKY MOUNTAIN SPOTTED FEVER: Ever since the settlement 
of Montana there has appeared in certain regions, particularly the Bitter Root 
Valley, a peculiar and very fatal disease of man. The disease was first recog- 
nized here about 1890. It is characterized by sudden onset, a high fever, severe 
arthritic and muscular pains, and a profuse petechial eruption in the skin, ap- 
pearing first on the ankles, wrists, and forehead but later usually spreading 
all over the body. In fatal cases the disease runs a rapid course, the patient 
dying from the sixth to the twelfth day. If the fever falls and the patient lives 
two weeks, recovery is usually rapid. There are two strains of the disease, a 
mild and a virulent type, and these appear to be present in most of the regions 
in which it occurs. The mortality rate varies from about 80 per cent for the 
virulent strain to about 4 to 6 per cent for the mild strain. This disease is 
designated "Rocky Mountain spotted fever" from its place of apparent origin. 
It is noncontagious, highly infectious, and transmitted to man by ticks. Wilson 
and Chowning (1902-1904) first advanced the theory that the disease was 
tick-borne and Ricketts (1906-1909) and his co-workers demonstrated that 
the disease is primarily an infection of small mammals (rodents) ; that large 
mammals, except man, are not susceptible; and that the tick, Dermacentor 
andersoni, is the transmitting agent for man. Wolbach (1919) described and 
named the parasite Dermacentroxenus ricfettsL For many years this disease 
was known only from a restricted area in the Rocky Mountain region. Rum- 
reich, Dyer, and Badger (1931) demonstrated the disease in the eastern 
United States and reported cases from rural areas in Delaware, Maryland, 
Pennsylvania, Virginia, North Carolina, and the District of Columbia during 
the summer of 1930. Later they proved that the vector was the dog tick, 
Dermacentor variabilis. Since then the disease has been found rather wide- 
spread throughout the United States. At present the disease is also known 
from western Canada (British Columbia and Alberta) and many parts of 
South America and Mexico. In South America this disease has been called 
exanthematic typhus of Sao Paulo, Tobia fever of Colombia, Choix or Pinta 



74 MEDICAL ENTOMOLOGY 

fever in Mexico, and Minas Geraes typhus in Brazil. The tick vector in South 
America is Amblyomma cajennense. 

The relation of ticks to this disease may be considered under two headings : 
maintenance in nature and transmission to man. 

MAINTENANCE IN NATURE : The following species of ticks are known to trans- 
mit, or can transmit experimentally, the rickettsiae among the reservoir 
hosts (mainly rodents) : Dermacentor andersoni (mainly by the larvae and 
nymphs) ; Dermacentor variabilis (all stages) ; Dermacentor occidentalis (all 
stages); Rhipicephalus sanguineus 3 (experimentally); Amblyomma ameri* 
canum (all stages); Amblyomma cajennense (experimentally and probably 
in nature); Ornithodoros par^eri (all stages experimentally); Ornithodoros 
nicollei (all stages, experimentally). In addition, all these ticks pass the rickett- 
siae through the eggs to their young so that the natural reservoir in rodents 
can be maintained or greatly increased. Another tick that is undoubtedly very 
important in many areas is the rabbit tick, Haemaphysalis leporis-palustris. 
This tick does not attack man, but it can transmit the rickettsiae from rabbit 
to rabbit and thus maintain an adequate source for those ticks that bite man 
and also feed on rabbits. 

TRANSMISSION TO MAN: Only those ticks that become infected and feed on 
man can transmit the disease. Dermacentor andersoni (adults) is the vector 
throughout its range (western Canada and western United States) ; Derma- 
centor occidentalis is probably a vector in the United States in western Cali- 
fornia and parts of Oregon; Amblyomma americanum (all stages) is a vector 
in some parts of the United States (known only at present as a vector in Texas 
and Oklahoma); in Brazil and Columbia Amblyomma cajennense is re- 
ported as the vector. In addition, other species may play a part as Ornithodoros 
parJ^eri, which Davis (1943) has shown to be an effective transmitter in all 
stages and through the egg even to the fourth generation. The same worker 
(1943) has shown that Ornithodoros nicollei is a good experimental vector of 
the rickettsiae of the spotted fevers of Brazil, Colombia, and Mexico in all 
stages and through the egg to the next generation. As this tick feeds readily 
on man and dogs, it is probably a vector in its range. 

The incubation period in man after infection by a tick varies from 2 to 
12 days. In recent years a vaccine has been developed that gives good promise. 
It is said to be erTective for nearly one year, and if it does not confer entire 
immunity it at least reduces to a minimum the danger of a fatal termination 
of the disease. 



3 Recently found naturally infected in Sonora, Mexico (Mariotte et a!. t 1945). 



THE ORDER ACARINA 75 

TULAREMIA: Tularemia is a plaguelike disease of rodents, particularly of 
rabbits and hares, caused by Pasteurdla tularensis (Bacterium tularense). The 
disease was discovered in rats in California by McCoy in 1910. The bacterium 
was isolated from squirrels and described by McCoy and Chapin in 1912. 
Francis (1919, 1920) demonstrated that the so-called "deer-fly fever" of man 
in Utah and the plaguelike disease of rodents are identical and caused by the 
same organism; he later (1921) named the disease "tularemia." The disease 
is highly infectious to man and is transmitted by various arthropods either by 
their bites, their crushed bodies, or their feces or by the tissues or body fluids of 
infected rodents; it is also occasionally water-borne. The disease is widespread 
in the United States and is reported from the following countries : Japan (1925), 
Russia (1928), Nor way (1929), Canada (1930), Sweden (1931), Austria (1935), 
Germany, Czechoslovakia, and Turkey (1936), Alaska (1937, no human cases 
but the organism was isolated from rabbit ticks), and from Tunisia. 

NATURAL RESERVOIRS: There are numerous natural reservoir hosts. Burroughs 
et al. (1945) list 44 hosts from the world, distributed among birds, insectivores, 
rodents, carnivores, and ungulates. They list 4 birds (ruffed grouse, bobwhite, 
sage hen, and horned owl), 3 carnivores (cat, dog, and coyote), 20 rodents, 
and sheep from the United States. Jellison and Parker (1945) present rather 
conclusive evidence that the main source of human infection in the United 
States is from cottontail rabbits (Sylvilagus spp.) particularly S. floridantis. Of 
the 14,000 cases reported in the United States (up to 1942) fully 90 per cent 
are traceable directly to infection from cottontail rabbits; only 40 cases oc- 
curred beyond the range of these rabbits. Jack rabbits are known reservoirs and 
are an indirect source of human infection through the agency of ticks and deer 
flies. In the same manner many rodents are indirect sources of human infection. 

TRANSMISSION TO MAN: Human infection is mainly through contact with 
reservoir hosts, particularly rabbits. The bacterium (Pasteurdla tularensis) is 
so infectious that it can pass directly through the human skin, and thus man 
is readily infected by handling infected animals, their flesh, or body fluids; by 
contact with the fecal wastes or body fluids of the vectors; by eating partially 
cooked infected rabbits, squirrels, and others; or by handling or drinking 
infected water. Jellison and Parker state that 90 per cent of the human cases 
in the United States result from handling infected rabbits; the other 10 per 
cent of the cases are traceable to handling other infected rodents, sheep, game 
birds, or other animals or by transmission by arthropods. Certain arthropods 
play an important part in maintaining this natural reservoir and also in trans- 
mitting the disease to man. Francis (1921) was the first to demonstrate the 



76 MEDICAL ENTOMOLOGY 

transmission of tularemia from infected animals (the jack rabbit) to man by 
the deer fly, Chrysops discalis (Fig. 161). Parker, Spencer, and Francis (1924) 
demonstrated that Dermacentor andersoni and Haemaphysalis leporis-palustris 
could transmit the disease and that the bacterium passes from stage to stage 
of the ticks. In 1926 Parker and Spencer reported the survival of the bacterium 
through the egg to the young of Haemaphysalis leporis-palustris and Derma- 
centor andersoni. Philip and Jellison (1934) showed stage-to-stage and 
generation-to-generation survival of this bacterium in Dermacentor variabilis. 
Dermacentor occidentalis and D. marginatus have also been shown to play 
some part in this disease complex. 

Although most of the human infection in North America is traceable to 
contact with rabbits, it must be borne in mind that ticks, particularly Hae- 
maphysalis leporis-palustris, Dermacentor andersoni, D. variabilis, and other 
bloodsucking arthropods, are of great importance in maintaining the disease 
among the natural reservoirs. Furthermore the disease can be water-borne as 
shown by Scott (1940) and Jellison et al. (1942) in the case of beavers and by 
Karpoflf and Antonoff (1936) in the case of water rats in Russia. In both in- 
stances the water was shown to be highly infectious when handled or drunk. 
Mosquitoes may also play a part in the infection of man and among the 
reservoir hosts, as shown by Philip (1932). 

* AUSTRALIAN "Q" FEVER, AMERICAN "NINE-MILE FEVER": 
"Q" fever was first recognized as a distinct entity by Derrick (1937) in Aus- 
tralia. It occurred among meat handlers and slaughterers in a restricted area 
about Brisbane. The causative organism was isolated and described as Ricfett- 
sia burneti by Burnet and Freeman (1937). "Nine-Mile fever" was recognized 
near Nine Mile Creek in Montana in 1938, and the infectious agent was iso- 
lated from the tick Dermacentor andersoni by Davis and Cox (1938); the 
human case (a laboratory worker) was described by Dyer (1938). Cox (1939) 
named the organism Ric^ettsia diaporica. It now seems well established that 
these two isolated diseases are identical. 4 In Australia the reservoir appears 
to be in bandicoot rats (Isodon torosus), three out of 103 tested being natu- 
rally infected. All species of bush animals tested proved susceptible to infection. 
The tick Haemaphysalis humerosa taken from bandicoots proved infectious, 
and bandicoots in certain areas showed a high agglutination rate (34 per cent). 
Although this tick does not normally bite man, it is suggested that it main- 
tains the reservoir and that Ixodes holocyclus (which readily bites bandicoots, 
man, and other animals) may transmit the disease among the bandicoots and 



4 Recently the generic name hds been changed to Coxiella. 



THE ORDER ACARINA 77 

to man. The rickettsiae develop in the epithelium lining of the gut of the tick 
so that the lumen and fecal wastes are heavily charged. The feces are highly in- 
fective, even when dry and powdery, to broken or injured skin. Transmission 
is only through fecal wastes of infected ticks entering the wound made by 
the bite or by the dry infective fecal wastes gaining access to wounds or by way 
of the respiratory tract. Other potential tick vectors are Haemaphysalis bispi- 
nosa and Rhipicephalus sanguincus. 

In North America Ric\ettsia diaporica has been isolated from Dermacentor 
andersoni in Montana and Wyoming, from Dermacentor occidentalis in 
Oregon and California, and from Amblyomma americanum in Texas (Lib- 
erty County). Davis (1943) demonstrated that Ornithodoros moubata could 
be infected by feeding on infected guinea pigs and could transmit the infec- 
tion by feeding up to 428 days following the infective feeding, and that trans- 
mission through the eggs was obtained to the F 2 generation. The infective 
agent was conserved in the tissues of the tick for at least 670 days. With O. 
hermsi transmission took place by feeding up to 772 days after the infective 
meal, and the infectious agent was conserved in the tissues for at least 979 days; 
there was no transmission through the egg. 

In Australia 176 cases in humans with three deaths are recorded up to 1942. 
In North America, cases (15, with one death in Washington, D.C.) have 
occurred in laboratory workers, and the infection is believed to be due to 
the inhalation of infected tick feces or dust from cultures while the persons 
were working with experimental animals. In cases involving the respiratory 
tract the disease is more serious. Recently an outbreak was reported at Amarillo, 
Texas, among slaughter-house workers (55 cases). Elkland (1947) records a 
case in Montana probably contracted from Dermacentor andersoni in the wild. 
Huebner et al. (1948) located an endemic center of "Q" fever in southern 
California (117 cases during 1947). They also report recovering Ric\ettsia 
burneti from raw milk in several dairies. Jellison and his co-workers (1948) 
recovered the organism Ricftettsia (Coxiella) burneti not only from raw milk 
but from butter made from unpasteurized milk. They also found the spinose 
ear tick, Otobius megnini (Duges), naturally infected. 

During World War II extensive outbreaks of "Q" fever occurred among 
Allied troops in Italy and Axis troops in the Balkans (Balkan grippe) and 
in Greece. Cases were also reported from ^Panama. Workers in research 
laboratories, especially among those handling the cultures of Ric^ettsia burneti, 
were infected. As a result of intensive studies of these outbreaks it seems estab- 
lished that there may be several strains of "Q" fever, but all appear to be identi- 
cal from the standpoint of reciprocal cross immunity, complement fixation, 



78 MEDICAL ENTOMOLOGY 

and agglutination absorption tests. Unfortunately nothing was learned re- 
garding the sources of the infection, the animal reservoirs, or the methods of 
transmission unless we accept the one known method the inhalation of the 
infectious agent (Amer. //. Hyg., 44, 1946). 

. COLORADO TICK FEVER: This disease is of unknown etiology. It is 
reported from various portions of the mountainous areas of Colorado, wide 
areas of Wyoming, and parts of Idaho. Parker et al. (1937) state that it was first 
observed in 1907 but not regarded as a distinct entity till 1930. The disease 
is associated with the bite of Dermacentor andcrsoni but is distinct from Rocky 
Mountain spotted fever; there is no rash and the fever is of the remittent type. 
The disease rarely proves fatal. 

' BULLIS FEVER: This peculiar disease is named after Camp Bullis in 
Texas, where the first cases were recognized by Woodland et al. (1943). In 
1943 over 485 cases were isolated among the troops; later Anigstein and Bader 
reported that some 1000 cases were observed. All reports indicate that the vector 
is the tick Amblyomma americanum, as practically all cases had numerous tick 
bites and this tick is the common and most abundant tick in the area and readily 
bites man. Steinhaus and Parker (1944) report a filter-passing agent from the 
tick Haemaphysalis leporis-palustris, taken from rabbits, but the authors do 
not conclude that this virus may be the causative agent of Bullis fever. 

. TICK TYPHUS: Tick typhus has been described from widely separated 
regions. The etiology of the disease is unknown. The disease is reported from 
Russia (central Siberia), where Bocharova (1945) reports that it is tick-borne 
and the vector Dermacentor nuttalli Olenev; he also found natural infection 
in this species in the wild. Natural infection was found in a number of rodents, 
including the domestic rat. Singh (1943) reports a case of typhus fever from 
Meerut, India, that Megaw (1943) calls a typical case of tick typhus. Walsh 
(1945) reports an epidemic of tick typhus in East Africa, and Tovar (1945) 
indicates that the disease is widespread in the Americas but not yet detected. 
It would seem that this disease entity is not well understood. Kenya tick 
typhus is said to be almost similar to boutonneuse fever. 

> BOUTONNEUSE FEVER (Fievre Exanth&natique de Marseille) : This 
disease was first reported from Tunisia by Conor and Bruch (1910). It is now 
known to occur all along the Mediterranean littoral from Portugal to Romania, 
and it has recently been reported from Ethiopia. The causative organism has 
been described by Brumpt (1932) under the name Ricfyttsia conori. This 
organism has been recovered from the tick Rhipicephalus sanguineus, which 



THE ORDER ACARINA 79 

is the known vector throughout the Mediterranean region. The reservoir hosts 
are the dog (most important), certain rodents as the spermophile Citellus citel- 
lus, the white rat, and mice. In the tick the rickettsia is transmitted from stage 
to stage and also through the egg to the larvae. The disease belongs to the 
"spotted-fever group." 

Kenya tick typhus is thought to be identical with boutonneuse fever, and 
Roberts (1935) has shown that Rhipicephalus sanguineus is the vector in 
Kenya of what is frequently called "tropical typhus." The etiological agent 
has been described as Rickettsia ricfyettsi conori. 

' SOUTH AFRICAN TICK-BITE FEVER: This disease is closely related 
to the spotted fevers and is caused by a rickettsia, variously known as Rickettsia 
ricfyettsi conori or as a distinct variety, R. r. pijperi. It was recognized as a dis- 
tinct clinical disease in South Africa sometime before 1930. Gear (1938, 1939) 
reports the disease in the Witwatersrand as severe, the reservoir being dogs 
and the vector the dog tick, Haemaphy 'salts leachi. Amblyomma hebraeum 
is also a vector, but it is stated that only the larval stage transmits the disease. 
The disease is nearly always associated with tick bites, the primary sore being 
described as a tache noire, and is accompanied by lymphadenitis. The dog tick, 
Haemaphysalis leachi, can transmit the disease in all stages and also by 
transovarial transmission through the egg; it is thus considered a reservoir 
of the disease. Rhipicephalus sanguineus is also reported as a potential 
vector. The distribution of the disease is not fully known. 

. RUSSIAN SPRING-SUMMER ENCEPHALITIS OR TICK-BORNE 
ENCEPHALITIS : This is the only human encephalitis known to be trans- 
mitted by ticks. It is recorded from parts of European Russia, Siberia, and 
parts of the maritime province of the Far East of Russia (always in well- 
demarcated virgin-forest regions). Various Russian investigators have shown 
that the tick Ixodes persulcatus Schulze is the natural vector. This tick occurs 
only in the forested regions, and the disease is transmitted to those who work 
in the forests. The tick has a two- or three-year cycle, and infection of the 
ticks occurs when they feed on the wild rodents that are the reservoirs. The 
virus is transmitted in the ticks from stage to stage and to the young through 
the eggs. Russian workers have shown that there are two peaks of infection, 
one in the spring and another in the summer. The first is from the feeding 
of the overwintering ticks, and the second is probably from the young that 
hatch from eggs laid during the spring months. There are indications that 
Dermacentor silvarum, Haemaphysalis concinna, and H. japonica may also 
serve as vectors since they have been found naturally infected. 



80 MEDICAL ENTOMOLOGY 

ST. LOUIS ENCEPHALITIS: See pages 95, 367. 
Animal Diseases 

In addition to the human diseases many diseases of domestic and game 
animals are also transmitted by ticks. A few of these may be mentioned here. 

PIROPLASMOSIS, RED-WATER FEVER, TEXAS FEVER, OR 
HEMOGLOBINURIA OF CATTLE: For a brief statement see page 58. 
In North America this disease (caused by Piroplasma bigemina) is transmitted 
by Boophilus annulatus; in Australia, the Philippine Islands, the Dutch East 
Indies, India, and parts of South America by Boophilus australis; and in South 
Africa by Boophilus decoloratus. Boophilus microplus is the vector in parts of 
South America, the West Indies, and probably other parts of the world. In 
East Africa this disease is also transmitted by Rhipicephalus appendiculatus 
and R. evertsi. In Europe a similar disease caused by Babesia bovis is trans- 
mitted by Ixodes ricinus. The etiological agent is transmitted from larva to 
nymph, from nymph to adult, and through the egg to the young. Malignant 
jaundice of dogs is a serious disease caused by Babesia cams and is transmitted 
by the brown dog tick (Rhipicephalus sanguineus) in the United States 
(Florida, where it was first discovered in North America in 1934), Asia, 
North Africa, and India; by Dermacentor reticulatus in Europe; and by 
Haemaphysalis leachi in South Africa. The parasite is passed by infected 
females through the egg to the larvae. "Carceag" of sheep and goats is caused 
by Babesia motasi. The disease occurs in eastern and southeastern Europe and 
its known vector is Rhipicephalus bursa, a one-host tick. The etiological agent 
is passed through the egg to the larvae, but infection is said not to take place 
till the tick has reached the adult stage on its host. Two diseases of horses 
are caused by species of Babesia. Babesia caballi is reported from southern and 
southeastern Europe and from the Caucasus region of Russia. The disease is 
very similar to Texas fever and Dermacentor reticulatus is the vector. Babesia 
equi occurs in southern Europe, Africa, southern Asia, and South America. 
In South Africa Rhipicephalus evertsi is the known vector. In adult horses 
and other members of the Equidae the disease (biliary fever) is highly virulent. 
Species of Babesia have been described from many other animals, but little 
is known about them or their vectors. 

ANAPLASMOSIS : Theiler (1910) recognized the small, coccuslike bodies 
on the periphery of many of the red blood cells of cattle suffering from a 
specific disease (now known as "anaplasmosis") and named them Anaplasma 
marginale. These had previously been seen by Smith and Kilborne (1893), 



THE ORDER ACARINA 81 

who did not correctly interpret them. In reality they had animals suffering 
from the two diseases, anaplasmosis and piroplasmosis. These two diseases are 
now well recognized, and anaplasmosis has been found in at least 22 states 
of our country as well as in South Africa. The disease is restricted to cattle 
. and frequently proves very serious, with a mortality varying from 5 per cent 
to over 50 per cent. Ticks are the important vectors, and numerous species 
have been incriminated. Rees (1934) lists the following: Boophilus annulatus, 
B. microplus, B. decoloratus, Dermacentor andersoni, D. variabilis, Hyalomma 
lusitanicum, Ixodes ricinus, I. scapularis, Rhipicephalus sanguineus, R. bursa, 
and R. simus. To these can be added Dermacentor occidentalis, D. albipictus, 
and some others of doubtful proof. At the present time only Boophilus annula- 
tus, Dermacentor andersoni, and D. occidentalis have been proved capable 
of transmitting the etiological agent to their offspring through the egg. In 
addition, many bloodsucking flies may act as mechanical carriers, such as 
the Tabanidae (at least seven species), and mosquitoes (several species). 
Probably one of the most important methods of transmission is from infected 
surgical instruments used in dehorning, bloodletting, castrations, etc. 

EAST COAST FEVER : A serious disease of cattle largely confined to the 
eastern coastal region of Africa though it is reported from India and Trans- 
caucasia is East Coast fever. It is caused by a minute protozoan, Theileria 
parva. This parasite occurs in the red blood cells, but the schizogonous cycle 
takes place in the spleen, lymph nodes, and some other organs. When the 
stage in the red blood cells is taken by ticks, particularly Rhipicephalus appen- 
diculatus, it undergoes a complicated life cycle in the tick and finally infected 
forms are found in the salivary glands (Cowdry, 1932). Transmission takes 
place when an infected tick feeds on a susceptible animal. There is no trans- 
ovarial passage of the parasite. Infection can pass from larvae to nymphs and 
nymphs to adults. Qtfier proven vectors are Rhipicephalus evertsi, R. simus 
(only in adults), and a Hyalomma species closely allied to impressum. 

FOWL SPIROCHETOSIS: This is a serious disease of fowls caused by 
Spirochaeta gallinarum Blanchard (marchouxi Nuttall). Its primary vector 
is the soft tick, Argas persicus. The disease is recorded from Brazil, Egypt, the 
Sudan, India, Australia, Europe (Germany), and the Transcaucasus region. 
The fowl mite, Dermanyssus gallinae, has been suspected as a vector, but 
the. work of Rastegaieff (1936) would seem to disprove this idea, though 
Hungerford and Hart (1937) indicate that this mite may serve as a mechani- 
cal transmitter. Zulzer (1937) states that mosquitoes (which species?) serve 
as vectors and that there is a cyclical development in them. 



82 MEDICAL ENTOMOLOGY 

OTHER DISEASES : There are other diseases of domestic animals which 
are transmitted by ticks, such as Nairobi sheep disease transmitted by Rhipi- 
cephalus appendiculatus and Amblyomma hebraeum, louping ill of sheep 
transmitted by Ixodes ricinus, heartwater of sheep, cattle, and goats in Africa 
transmitted by Amblyomma hebraeum and A. variegatum, and some others 
about which little is known. 

TICK CONTROL 

At the present time no adequate specific treatments are known for tick-borne 
diseases of man and animals except for the relapsing fevers of man. The in- 
travenous injection of neoarsphenamine or other arsenic compounds usually 
brings about the complete elimination of the spirochetes of relapsing fevers. 
However, the disease runs a tedious course, and prophylactic measures are to 
be preferred rather than treatment after infection. In the case of malignant 
jaundice of dogs (caused by Babesia cants) and in illnesses caused by some of 
the other larger species of Babesia, the administration of Trypan Blue is known 
to give good results. Such treatments cannot be applied to dogs, cattle, or 
horses except in the case of very valuable animals. In general, it may be stated 
that the control of ticks is the most essential and effective method of keeping 
these diseases in check. However, the development of vaccines and serum 
treatments should prove of great value, and much progress may be looked for 
in these fields. 

On domestic animals, as cattle, horses, dogs, etc., the most efficient method 
of destroying ticks is by dipping or spraying. The dip or spray employed is 
usually an arsenical one. Each country has its own official dip. That recom- 
mended by the United States Department of Agriculture is as follows: 

Sodium bicarbonate 24 pounds 

Arsenic trioxide (white arsenic) 8 pounds 

Pine tar i gallon 

Water 500 gallons 

This material is prepared in a large dipping vat. The vat is so arranged that 
the cattle are driven into it one by one, swim through it, and walk out at the 
other end by means of an inclined, cleated plane. They are then held a short 
time in a dripping pen, the drip running back into the vat. By consistent pe- 
riodic treatments large areas have been completely cleared of cattle ticks, as 
for instance most of the southern United States. 

However, the problem of controlling such ticks as Ornithodoros spp., Argas 
spp., and those that normally attach only to wild animals is a much more 





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? ^ s " 1 
S I^.g. 3-| 

s t -g ^ 's <x 5? 

- Q 9 Q S 
CQ ^ 'c; * ^ 


| | 


lis 

III 






marginatu 


Dermacentor t 


i- 

S- 3 

<o O 
. 

-^ c 

c< O 


Amblyomma 
A. variegatum 


, 'C x ^ a ^ ^ S 

11 ills 

s^iti *? 

i<o SS^S4 


l| 1 

ii 5 o 


Rhipicephalus 
Amblyomma 
Rhipicephalus 


Ixodes ricinus 


Argas persicus 


Dermacentor 






5 




s 








:s 


V) 


& 


iT ^ 


"5 "^ 


rt 


rt 


a 


a 


>-, 


8 


o 


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<L> 


4J 


2 | 


E 


R 


-G 


3 n -5 


<-i_i ^ 





-3 


"S 


5 -J 


"rt 


Horse piroplasi 
Babesia caballi 


Biliary fever of 
Babesia equi 


Heartwater of * 
sheep, and goat 
Ricf(ettsia rum, 


Q 

.2 5 
3 * 
% g 

If 
a c 

< ^ 


East Coast fever 
Theileria parva 


0, 
^ g 


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od 





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(S 


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86 MEDICAL ENTOMOLOGY 

difficult one. Many of these ticks are not known to act as vectors of disease- 
producing organisms, but others, as Haemaphysalis Ieporis-pali4stris, serve as 
agents in maintaining the natural reservoir. Ornithodoros moubata, which 
lives principally in and around human habitations, can probably be effectively 
controlled by proper housing and cleanliness. In the case of the two- or three- 
host ticks that live primarily on wild animals we have little knowledge or 
experience on which to base control measures. The only large-scale work car- 
ried on is that against Dermacentor andersoni in parts of Montana. Here the 
natural reservoir of the human disease, Rocky Mountain spotted fever, is the 
native rodents. The main efforts have been directed toward the destruction 
of the rodent hosts (squirrels, ground squirrels, rabbits, etc.) by means of 
poison baits and the killing of the adult ticks by the dipping of horses and 
cattle. By destroying the hosts of the larvae and nymphs it is hoped to starve 
out the ticks. Though this work has proved somewhat successful, it is difficult 
to see how it could be employed for many tick species. Recently a tick parasite, 
Ixodiphagtts cauctirtei du Buysson, was discovered in France and has been 
introduced into Montana and the eastern United States. The parasite is known 
to attack a number of different species of ticks. It is hoped that the employ- 
ment of this parasite on a large scale may bring about a decided reduction in 
the disease-distributing species of ticks. 

Personal prophylaxis must be relied on as the most effective means of 
avoiding tick-borne diseases. In tick-infested regions sleeping or sitting on 
the ground should be avoided, and camping places should be selected with 
care. The use of suspended hammocks for sleeping purposes is most essential. 
The clothing should be rather coarse and loose and the legs well protected 
by laced high boots or wrap puttees. Before entering dwellings or prepared 
camps for the night, all clothing should be carefully examined and adhering 
ticks destroyed. If convenient, a complete change of clothing is the wisest 
precaution. Each evening the clothing worn during the day should be care- 
fully examined for adhering ticks. Only by careful attention can infestation 
by ticks be avoided. This is well illustrated in the case of Dermacentor ander- 
soni. Though the most exacting precautions have been observed in the tick- 
control work in Montana, yet at least five men have died through contracting 
the disease in some unknown manner. 

Since the discovery of the effectiveness of various DDT combinations in 
controlling mosquitoes, lice, fleas, and other insects, experiments have been 
conducted with this material against ticks. Areas infested with various species 
of ticks have been sprayed, but the results are not very gratifying. A certain 
amount of control is indicated with such species as Dermacentor variabilis 



THE ORDER ACARINA 87 

and Amblyomma americannm. Fair control of Rhipicephalus sanguineus has 
been obtained when 10 per cent DDT dusts have been applied in houses. In 
all probability some effective agent against ticks may be developed. No satis- 
factory repellent has been developed. 

REFERENCES 5 

American Association for the Advancement of Science. A symposium on relapsing 

fever in the Americas. (Pub. 18) Washington, D.C., 1942. 

. Rickettsial diseases of man. Washington, D.C., 1948. (A symposium.) 

*Aragao, H. de B. Ixodidas brasileiros e de alguns paizes limitrophes. Mem. do 

Instit. Oswaldo Cruz, 31: 769-843, 1936. 
Arthur, D. R. The feeding mechanism of Ixodes ricinus L. Parasitology, 37: 

154-161, 1946. 
Badger, L. F., and Dyer, R. E. An infection of the Rocky Mountain fever type. 

U.S. Pub. Hlth. Repts., 49: 463-470, 1931. 
*Banks, N. A. A revision of the Ixodidae, or ticks, of the United States. U.S. 

Dept. Agr., Div. Ent., Tech. Ser. 15, 1908. 
Bates, L. B., Dunn, L. H., and St. John, J. H. Relapsing fever in Panama. Amer. 

Jl. Trop. Med., i: 183-210, 1921. 
Bedford, G. A. A synoptic check list and hosts of the ectoparasites found in South 

African mammalia. i8th Rept. Dir. Vet. Serv. and Animal Ind., Union of 

South Africa, pp. 223-523, 1932. Onderstepoort Jl. Vet. Sci. and Animal Ind., 

7 (Suppl. i): 69-110, 1936. 
Bequaert, J. Synopsis des tiques du Congo beige. Rev. Zool. Bot. Afr., 20: 209- 

251, 1931. 
. The ticks or Ixodoidea of the northeastern United States and eastern Canada. 

Entomologica Americana, 25: 73-232, 1946. 
Bertram, D. S. The structure of the capitulum in Ornithodoros. Ann. Trop. Med. 

Parasit., 33: 229-258, 1939. 
Bishopp, F. C. Ticks and the role they play in the transmission of diseases. Rept. 

Smithsonian Inst. for 1933, pp. 389-406, 1935. 
, and Trembley, H. L. Distribution of certain North American ticks. Jl. 

Parasit., 31: 1-54, 1945. 
, and Wood, H. P. The biology of some North American ticks of the genus 

Dcrmacentor. Parasitology, 6: 153-187, 1913. 
Burnet, F. M., and Freeman, M. Experimental studies on the virus of "Q" fever. 

Med. Jl. Australia, 2: 299-305, 1937. 
Burroughs, A. R., et at. A field study of latent tularemia in rodents with a list of 

all known naturally infected vertebrates. Jl. Inf. Dis., 76 (2): 115-119, 1945. 

5 This is only a partial list. Articles with bibliographies are starred; with extensive 
bibliographies, double-starred. 



88 MEDICAL ENTOMOLOGY 

Christophers, S. R. The anatomy and histology of ticks. Sci. Mem. Med. and 

Sank. Depts. India, n.s. 23, 1906. 
Chumakov, M. P. Further study of the area of distribution and peculiarities of 

the epidemiology of tick-borne encephalitis in the European part of the U.S.S.R. 

In Russian. Summary in Rev. Appl. Ent. (B): 117, 1946. 
Cogswell, W. F. Tick paralysis. Mont. State Bd. Hlth., Spl. Bull. 26: 47-49, 

1923. 
Cooley, R. A. The genera Dermacentor and Otocentor (Ixodoidea) in the United 

States. Nat. Inst. Hlth. Bull. 171, 1938. 

- . Determination of Ornithodoros species. In Symposium on relapsing fevers 
in the Americas. Amer. Assoc. Adv. Sci., Pub. 18: 77-84, 1942. 

- . The genera Boophilus, Rhipicephalus and Haemaphysalis (Ixodoidea) of 
the new world. Nat. Inst. Hlth., Bull. 187, 1946. 

- , and Kohls, G. M. The Argasidae of North America, Central America and 
Cuba. Amer. Mid. Natural., Monograph i, 1944. 

- , and Kohls, G. M. The genus Amblyomma in the United States. Jl. Parasit., 
30: 77-1 1 1, 1944. 

Cox, H. R. Ricfettsia diaporica and American "Q" fever. Amer. Jl. Trop. Med., 

20: 463-469, 1940. 
Cunlifle, N., and Nuttall, G. H. F. Some observations of the biology and structure 

of Ornithodoros moubata Murray. Parasitology, 13: 327-347, 1921. 
Davis, Gordon E. Ornithodoros par^cri; distribution and host data; spontaneous 

infection with relapsing fever spirochetes. U.S. Pub. Hlth. Repts., 54: 1345- 



- . Bacterium tularense: its persistence in the tissues of the argasid ticks Ornitho- 
doros turicata and O. parferi. Ibid., 55: 676-680, 1940. 

- . Ornithodoros par\eri Cooley: observations on the biology of this tick. Jl. 
Parasit., 27: 425-433, 1941. 

- . Tick vectors and life cycles of ticks. In Symposium on relapsing fever in 
the Americas. Amer. Assoc. Adv. Sci., Pub. 18: 67-76, 1942. 

- . Studies of the biology of the argasid tick, Ornithodoros nicollei Mooser. Jl. 
Parasit., 29: 393-395, 1943. 

- . Relapsing fever: the tick, Ornithodoros turicata as a spirochaetal reservoir. 
U.S. Pub. Hlth. Repts., 58: 839-842, 1943. 

- . American Q fever; experimental transmission by the argasid ticks Ornitho- 
doros moubata and O. hermsi. Ibid., pp. 984-987, 1943. 

- . The tick Ornithodoros rudis as a host to the rickettsiae of the spotted fevers 
of Colombia, Brazil and the United States. Ibid., pp. 1016-1020, 1943. 

- . Experimental transmission of the rickettsiae of spotted fevers of Brazil, 
Colombia and the United States by the argasid tick, Ornithodoros parpen. Ibid., 
pp. 1201-1208, 1943. 

- . Experimental transmission of the richettsiae of spotted fevers of Brazil, 



THE ORDER ACARINA 89 

Colombia and the United States by the argasid tick, Ornithodoros nicollei. 

Ibid., pp. 1742-1744, 1943. 
Derrick, E. H. "Q" fever, a new fever entity. Med. Jl. Australia, 2: 281-299, T 937* 

. Ricfettsia burnetl: the cause of "Q" fever. Ibid., p. 14, 1939. 

. The epidemiology of "Q" fever. Jl. Hyg., 43: 357-361, 1944. 

Dios, R. L., and KnopofI, R. Sobre Ixodoidea de la Republica Argentina. Rev 

Inst. Bact. (Buenos Aires), 6: 359-412, 1935. 
Dunn, L. H. The ticks of Panama, their hosts, and the diseases they transmit. 

Amer. Jl. Trop. Med., 3: 91-104, 1923. 
. Notes on two species of South American ticks, Ornithodoros talaje Guerin- 

Men. and 0. venezuelensis Brumpt. Jl. Parasit., 13: 177-182, 1927. 
. Studies on the South American tick, Ornithodoros venezuelensis, in Colom- 
bia. Ibid., pp. 249-255, 1927. 
**Eysell, Adolf. Zecken. In Handbuch der Tropenkrankheiten, edited by Carl 

Mense, i : 1-40, 1924. 
Fairchild, G. B. An annotated list of blood-sucking insects, mites, and ticks from 

Panama. Amer. Jl. Trop. Med., 23: 569-591, 1943. 
Ferguson, E. W. Deaths from tick paralysis in human beings. Med. Jl Australia, 

2(i4) : 346-34^ I9 2 4- 
*Fielding, J. W. Australasian ticks. Ser. Pub. (Trop. Div.) Australia Dept. 

Hlth., No. 9, 1926. 
*Fotheringham, W., and Lewis, E. A. East coast fever; its transmission by ticks 

in Kenya Colony. Parasitology, 29: 504-523, 1937. 
Francis, Edward. Microscopic changes of tularaemia in the tick, Dermacentor 

under sonl, and the bedbug, Cimex lectularius. U.S. Pub. Hlth. Repts., 42: 

2763-2772, 1927. 
* . Arthropods in the transmission of tularaemia. Trans. 4th Internat. Cong. 

Ent., 2: 929-944, 1929. 
. The longevity of fasting and non-fasting Ornithodoros turicata and the 

survival of Spirochaeta obcrmclerl within them. In Symposium on relapsing 

fever in the Americas. Amer. Assoc. Adv. Sci., Pub. 18: 85-88, 1942. 
, et al. Tularaemia Francis, 1921: a new disease of man. U.S. Pub. Hlth. 

Serv., Hyg. Lab. Bull. 130, 1922. A series of articles by Francis and his as- 
sociates. 
Gear, J., and de Meillon, B. The common dog tick, Haemaphy sails leachl as a 

vector of tick typhus. S. Afr. Med. JL, 13: 815-816, 1939. 
Graybill, H. W. Studies on the biology of the Texas-fever tick. U.S. Dept. Agr., 

Bur. Animal Ind., Bull. 130, 1911. 
Green, R. G. Virulence of tularaemia as related to animal and arthropod hosts. 

Amer. Jl. Hyg., 38: 282-292, 1943. 
, et al. A ten-year population study of the rabbit tick, Haemaphysalis leporis- 

palustrls. Ibid., pp. 260-281, 1943. 



9 o MEDICAL ENTOMOLOGY 

Hadwen, Seymour. On "tick paralysis" in sheep and man following bites of 
Dermacentor venustus, with notes of the biology of the tick. Parasitology, 
6: 283-297, 1913. 

, and Nuttall, G. H. F. Experimental "tick paralysis" in the dog. Ibid., 

6: 298-301, 1913. 

Hammon, W. McD. The arthropod-borne encephalitides. Amer. Jl. Trop. Med., 

28: 515-525* J 94 8 - 
Hooker, W. A., Bishopp, F. C., and Wood, H. P. The life history and bionomics 

of some North American ticks. U.S. Dept. Agr., Bur. Ent., Bull. 106, 1912. 
Howard, C. W. A list of the ticks of South Africa, with descriptions and keys 

to all of the forms known. Ann. Transvaal Mus. (Pretoria), i: 73-170, 1908. 
Huebner, R. J. Report of an outbreak of "Q" fever at the National Institute of 

Health. Amer. Jl. Hyg., 37: 431-440, 1947. 
, et al. "Q" fever studies in southern California. U.S. Pub. Hlth. Repts., 

63: 214-222, 1948. 
, Jellison, W. L., and Beck, M. D. Q fever a review of current knowledge. 

Ann. Intern. Med., 30: 495-509, 1949. 
*Hunter, W. D., and Bishopp, F. C. The Rocky Mountain spotted fever tick. 

U.S. Dept. Agr., Bur. Ent., Bull. 105, 1911. 
** , and Hooker, W. A. Information concerning the North American fever 

tick, with notes on other species. Ibid., Bull. 72, 1907. 
Jellison, W. L. The geographical distribution of Rocky Mountain spotted fever 

and Nuttall's cottontail in the western United States. U.S. Pub. Hlth. Repts., 

60: 958-961, 1945. 
, and Parker, R. R. Rodents, rabbits and tularaemia in North America. 

Amer. Jl. Trop. Med., 25: 349-362, 1945. 

, et al. Epizootic tularaemia in the beaver, Castor canadensis, and the con- 
tamination of stream water with Pastcurdla tularcnsis. Amer. Jl. Hyg., 36: 168- 

182, 1942. 
, et al. Occurrence of Coxiella burneti in the spinose ear tick, Otobius 

megnini. U.S. Pub. Hlth. Repts., 63: 1483-1489, 1948. 
, et al.^ Recovery of Coxiella burneti from butter made from naturally infected 

and unpasteurized milk. Ibid., 63: 1712-1713, 1948. 
Lahille, F. Contribution a 1'etude des Ixodides de la Republique Argentine. 

Anales Ministero Agr., seccion de Zootechnia, Bact., Veterin. y Zool., 2: 1-166, 

1905. 
Lewis, E. A. A study of the ticks of Kenya Colony. Bull. Dept. Agr. Kenya, 

No. 7, 1934. 
. The ticks of East Africa. Emp. Jl. Exp. Agr., 7 (27) : 261-270; 7 (28) : 299- 

3<>4> 1939- 
McCaffrey, D. The effects of tick bites on man. Jl. Parasit., 2: 193-194, 1916. 



THE ORDER ACARINA 91 

McCormack, P. D. Paralysis in children due to the bites of wood ticks. Jl. Amer. 
Med. Assoc., 77: 260-263, 1921. 

MacLeod, J. Ixodcs ricinus in relation to its physical environment. Parasitology, 
26: 282, 1934; 27: 123-144, 489-500, 1935; 28: 295-319, 1936. 

Mail, G. A., and Gregson, J. D. Tick paralysis in British Columbia. Jl. Canad. 
Med. Assoc., 39: 532-537, 1938. 

Mariotte, C. O., et al. Hallazgo del Rhipicephalus sangulneus Latreille infectado 
naturalmente con fieber manchada de las Montanas Rocosas en Sonora (Mexico). 
Rev. Inst. Salub. y Enferm. Trop., 5: 297-300, 1944. 

Mazzotti, L. Transmission experiments with Spirochaeta turicata and S. vene- 
zudcnsis with four species of Ornithodoros. Amer. Jl. Hyg., 38: 203-206, 1943. 

Milne, A. The ecology of the sheep tick, Ixodes ricinus L. Parasitology, 36: 142- 
*57> J 945; 3 8: 27-50, 1947. 

Moilliet, T. K. A review of tick paralysis in cattle in British Columbia. Proc. 
Em. Soc. B.C., 33: 35-39, 1937. 

Neumann, L. G. Ixodidae. In Das Tierrich, Lieferung 26, 1911. 

Newstead, R. Ticks and other blood-sucking Arthropoda (in Jamaica). Ann. 
Trop. Med. Parasit., 3: 421-469, 1909. 

Nuttall, G. H. F. The Ixodoidea or ticks, spirochaetosis in man and animals, 
piroplasmosis. The Harben Lectures, 1908. Jl. Roy. Inst. Pub. Hlth., July, 
Aug., and Sept., 1908. 

. On symptoms following tick-bites in man. Parasitology, 4: 80^-93, 1911. 

. Tick paralysis in man and animals. Ibid., 7: 95-104, 1914. 

, Cooper, W. F., and Robinson, L. The structure and biology of Haemaphy- 

sails punctata Cancstrini and Fanzago. Ibid., i: 152-180, 1908. 

** , Warburton, C., et al. A monograph of the Ixodoidea.' Part i. Argasidae, 

1908. Part 2. Sect, i, Classification; Sect, n, The genus Ixodes, 1911. Part 3. The 
genus Haemaphysalis, 1915. Part 4. The genus Amblyomma (by L. E. Robin- 
son), 1926. (This work constitutes the outstanding contribution to our knowl- 
edge of the ticks. Bibliographies complete and extensive. Beautifully illus- 
trated with colored plates and line drawings.) 

Parker, R. R. Quail as a possible source of tularaemia infection in man. U.S. 
Pub. Hlth. Repts., 44: 999-1000, 1929. 

. Rocky Mountain spotted fever. Mont. State Bd. Ent., 7th Biennial Rept., 

pp. 39-62, 1929. 

, and Kohls, G. M. American Q fever; the occurrence of Rict^cttsia disporlca 

in Amblyomma amcricanum in eastern Texas. U.S. Pub. Hlth. Repts., 58: 
1510-1511, 1943. 

, Philip, C. B., and Davis, G. E. Tularaemia. Ibid., 47: 479-487, 1932. 

' , Philip, C. B., and Jellison, W. L. Rocky Mountain spotted fever. Amer. 

Jl. Trop. Med., 13: 341-379* '933- 



**. 



92 MEDICAL ENTOMOLOGY 

Parker, R. R., and Spencer, R. R. Hereditary transmission of tularaemia infection 

by the wood tick, Dermacentor andersoni Stiles. U.S. Pub. Hlth. Repts., 41: 

1403-1407, 1926. 
, and Steinhaus, E. A. American and Australian Q fevers. Ibid., 58: 523- 

527, 1943. 
** , et al. Ticks of the United States in relation to disease in man. Jl. Econ. 

Ent., 30: 51-69, 1937. 
**"Q" fever. Amer. Jl. Hyg., 44, 1946. (All of No. i is devoted to articles on 

this disease by numerous authors.) 
*Rees, C. W. Transmission of anaplasmosis by various species of ticks. U.S. 

Dept. Agr., Tech. Bull. 418, 1934. 
Robinson, L. E., and Davidson, J. The anatomy of Argas persicus (Oken 1818). 

I III. Parasitology, 6: 20-48, 217-256, 382-424, 1914. 
Ross, I. C. The bionomics of Ixodes holocyclus Neumann, with a redescription 

of the adult and nymphal stages and a description of the larvae. Ibid., 16: 365- 

381, 1924. 
. An experimental study of tick paralysis in Australia. Ibid,, 18: 410-429, 

1926. 
Rumreich, A., Dyer, R. E., and Badger, L. F. The typhus-Rocky Mountain 

spotted fever group. U.S. Pub. Hlth. Repts., 49: 470-480, 1931. 
*Salmon, D. E., and Stiles, C. W. The cattle ticks (Ixodoidea) of the United 

States. U.S. Dept. Agr., Bur. Animal Ind., i7th Rept., pp. 380-491. 
Samson, K. Zur Anatomic und Biologic von Ixodes ricinus L. Zeit. Wiss. Zool., 

93: 185-236, 1909. 

Sen, S. K. The mechanism of feeding in ticks. Parasitology, 27: 355-368, 1935. 
Silber, L. A., and Shubladze, A. K. Louping-ill in the USSR. Amer. Rev. Sov. 

Med., 2: 339-341, 1945- 
Smith, C. N., Cole, M. M., and Gouck, H. K. Biology and control of the American 

dog tick. U.S. Dept. Agr., Tech. Bull. 905, 1946 
Smith, D. J. W. Studies in the epidemiology of "Q" fever. Aus. Jl. Exp. Med. 

Sci., 20: 213-217, 1942. 
Smith, T., and Kilbourne, F. L. Investigations into the nature, causation, and 

prevention of Texas or southern cattle fever. U.S. Dept. Agr., Bull, i, 1893. 
Stiles, C. W. The taxonomic value of the microscopic structure of the stigmal 

plates in the tick genus Dermacentor. Pub. Hlth. and Marine-Hosp. Serv., U.S. 

Hyg. Lab., Bull. 62, 1910. 
Todd, J. L. Tick paralysis. Jl. Parasit., i: 55-64, 1914. 

. Tick caused paralysis. Jl. Canad. Med. Assoc., 9: 994-996, 1919. 

Toumanofi, C. Les Tiques (Ixodoidea) de 1'Indochine. Inst. Pasteur Indochine, 

Saigon, 1944. 
Warren, Joel. Epidemic encephalitis in the Far East. Amer. Jl. Trop. Med., 26: 

417-436, 1946. 



THE ORDER ACARINA 93 

Weller, B., and Graham, G. M. Relapsing fever in central Texas. Jl. Amer. Med. 

Assoc., 95: 1834-1835, 1930. 
Wheeler, C. M. A contribution to the biology of Ornlthodoros hermsi Wheeler, 

Herms and Meyer. Jl. Parasit., 29: 33-41, 1943. 
*Wolbach, S. B. Studies on Rocky Mountain spotted fever. Jl. Med. Res., 41: 

1-197, 1919. 



CHAPTER IV 



The Order Acarina; Parasitoidea, 

Sarcoptoidea, Trombidoidea, 

Tarsonemoidea, Tyroglyphoidea, 

and Demodicoidea 



THE PARASITOIDEA 

THE Parasitoidea contain at least three rather large families. Their struc- 
ture allies them with the ticks. Tracheae are present and open through 
a pair of spiracles located on spiracular plates placed usually ahove and be- 
tween the third and fourth coxae. The mouth parts are well developed and 
consist of chelate or piercing chelicerae, an unarmed hypostome, and a pair 
of small palpi. The ventral surface lacks furrows, but sclerotized plates are 
generally present. Only one family, the Dcrmanyssidae, is of interest here. 
The members of this family may be recognized as they are all true parasites 
of reptiles, birds, and mammals. The chelicerae are needlelike or shearlike, 
usually without teeth. Ventral and anal plates are nearly always present and 
separate; a dorsal plate is present but covers only a part of the body. Only 
two genera of this large family are known to contain species that may attack 
man or be found associated with the transmission of disease. These two 
genera may be separated by the following couplet : 

1. Chelicerae shearlike, both arms present (Fig. 26) Liponyssus l 

2. Chelicerae needlelike and long (Fig. 26) Dermanyssus 



1 This genus and a number of related genera were separated by Ewing (1923) and 
placed in a subfamily, Liponyssinae; later Vitzthum (1931) created the family Uponys- 
sidae for these genera; recently da Fonseca (1948) changed the family name to Macronys- 
sidae. 



THE ORDER ACARINA 



95 



Dermanyssus gallinae (Linn.) is the common chicken mite (Fig. 27). It is 
bloodsucking in habit and usually feeds at night when the fowls are roosting. 
The mites engorge rapidly and leave their hosts to spend the day hidden away 
in cracks, crevices, and trash about poultry houses. The eggs are laid in the 
trash and rubbish; they hatch in three to four days. The larval and nymphal 
life occupies ten days to two weeks. The mites will attack persons handling 
infested fowls or sleeping in or near infested poultry houses. Though the 
mites cause a marked dermatitis in humans, it is said they do not obtain 




Fig. 26. (A) Chelicera of Liponys- 
sus bacoti. (B) Chelicera of Derma- 

nyssus gallinae. 



Fig. 27. Dermanyssus gallinae, the 
chicken mite. Dorsal view. (After 
Ewing.) 



human blood. Avoidance of the mites is all that is necessary to reduce the 
dermatitis as they dc not live long on the human body. Recently it has been 
shown by Smith et al. (1944, 1945, 1946) that the chicken mite appears to be 
the natural transmitter and reservoir of the St. Louis encephalitis virus among 
chickens. Furthermore these workers demonstrated that the virus is passed 
through the eggs to the offspring of the mites. As chickens are also reservoirs 
of this virus and as Culex pipiens (the common house mosquito) is a common 
feeder on chickens and on man, it is well established that this mosquito is an 
important vector of this disease to man. Here we have the complex of the 
chicken mite maintaining the virus in chickens and the mosquito (Culex 
pipiens) transferring the virus to man. The mosquito may also serve as a 



96 MEDICAL ENTOMOLOGY 

vector from chicken to chicken. An adequate control o the chicken mite 
might aid in the reduction of the incidence of this disease among men. 
Howitt et al. (1948) recovered the virus of eastern equine encephalomyelitis 
from Dermanyssus gallinae taken in nature in Tennessee; they also isolated 
the virus in the chicken lice, Menopon pallidum Nitsch. and Eomenacanthus 
stramineus (Nitsch.) taken from poultry. This is the first recovery of this virus 
from insects in nature. 




Fig. 28. Dermanyssus (Allodermanyssui) sanguineus. Lcff: Ventral view of female. 
Right: Dorsal view of female. (Redrawn and modified from H'rst.) 

Dermanyssus (Allodermanyssus) sanguineus Hirst is a parasitic mite on 
rats and mice. It was described from Egypt in 1914. The female can be easily 
separated from D. gallinae by the possession of two dorsal shields, the posterior 
one being small and circular (Fig. 28). D. sanguineus was first reported from 
America in 1923 by Ewing, though collected in Washington in 1909. At 
present it is known from New York, Philadelphia, Boston, 'Indianapolis, and 
Tucson as well as from Washington, D.C. In 1946 a peculiar* febrile disease of 
unknown etiology appeared in parts of New York City. Huelbner et al. (1946) 
reported this disease (Rickettsialpox) as due to a rickettsia, \Vhich he named 

\ 



THE ORDER ACARINA 97 

Rickettsia a\ari. This rickettsia was recovered from the mite and from patients 
suffering from the disease; mice were infected by mites carrying the rickettsia. 
During the summer of 1946 over 100 cases of human infection were reported 
from New York City. 

Liponyssus bursa (Berlese) and Liponyssus sylviarum Canestrini and Fan- 
zago are mites that commonly infest poultry, and man may be attacked 
when handling infested birds. L. bacoti (Hirst) is frequently called the tropi- 
cal rat mite (Fig. 29) as it was originally described from Egypt and was 
thought to be mainly distributed in tropical countries. It is now known to be 




Fig. 29. Liponyssus bacoti, the tropical rat mite. Dorsal and ventral views. (After Dove 
and Shelmire, Journal of Parasitology,) 

widely distributed in many parts of the world including the United States. In 
America it is known from many states and occurs at least as far north as New 
York and Minnesota, This mite is primarily a parasite of rats, but it readily 
attacks man, especially in such places as buildings, granaries, storehouses, pub- 
lic buildings, stores, or even private homes where rats are abundant. The mite 
feeds only on blood. The nymphs and adults drop from their hosts after 
each blood meal; thus the mite may feed on a variety of different animals 
during its life cycle. This feeding habit is well adapted to the transmission of a 
blood virus or parasite. The life cycle is comparatively short. The eggs hatch 
in about four days and the adult stage may be attained 12 days later. Dove and 
Shelmire found that at least four blood meals are necessary to rear a larva to 



98 MEDICAL ENTOMOLOGY 

the adult stage. The only known way to control the mites is to destroy the rats. 
DDT might prove an effective control method in rat-infested buildings 
where killing of the rats is not feasible. 

Shelmire and Dove (1931) described a large number of cases of dermatitis 
caused by this mite. The eruptions appeared as urticarial wheals varying in 
size from that of a pinhead to that of a split pea. On children urticarial welts, 
papules, and vesicles are often present. Severe pruitus may result, and sec- 
ondary infections may occur from scratching. The author has received several 
reports of severe infestations of this mite in large manufacturing plants in New 
York state. The mites gradually disappeared with the destruction of the rats. 

The above authors also proved experimentally, with rats and guinea pigs, 
that this mite can transmit endemic (murine) typhus. They showed that the 
infection in mites is transmitted to their offspring, the young larvae from 
infected mothers producing typical murine typhus in guinea pigs by their 
bites. Later they demonstrated that the mite is capable of maintaining the 
infection in wild rats and concluded that rats are important reservoirs of 
murine typhus, a fact that is now well known. 

Philip and Hughes (1948) have demonstrated that this mite can transmit 
experimentally rickettsialpox (Rickettsia afari) and have presented data that 
indicate transovarial transmission of the parasite. 

THE SARCOPTOIDEA 

This superfamily is restricted to atracheate mites, parasitic on animals, 
mainly birds, mammals, and insects. Many of the external structures generally 
found in mites are greatly reduced or lacking. The mouth parts arc modified 
and reduced so that the parts cannot be distinguished easily (Fig. 30). The 
palpi, so prominent in the ticks, are almost lacking in segmentation and are 
often more or less fused with the mouth parts. The chelicerae are reduced to 
mere sclerotized rods or blades; a hypostome is lacking. The skin of the 
body is marked with fine parallel folds, and it bears, especially on the dorsal 
surface, minute setae, stout spines, and cones or modifications of them. The-- 
legs are short and frequently modified for clasping. Usually the legs, or some 
of them, terminate in a stalked sucker or long hair. The two anterior pairs 
are widely separated from the two posterior pairs. 

The sarcoptoid mites live on their hosts throughout their life, mating and 
egg laying taking place on their hosts. They infest the skin, tissues, hairs, or 
feathers of their hosts. Sexual dimorphism is usually marked, the males pos- 
sessing special structures for clasping or holding the females. The principal 



THE ORDER ACARINA 99 

families may be separated by the following key (adapted from Banks and 
Ewing) : * 

KEY TO FAMILIES OF SARCOPTOIDEA 

i. With special apparatus for clinging to hairs, usually either modified 
legs or chelicerae. Parasitic on mammals. (Contains no species of 

known medical importance) Listrophoridae 

No such special clinging apparatus 2 



---Ch 




Ar- 




Fig. 30. Lefl: Dorsal view of capitulum of Psoroptes communis var. 
cuniculi. Right: A single chelicera, greatly enlarged. Ar, articulation 
of internal part of chelicera; BC, basis capitulum; C, Chi, Chz, cheli- 
cerae; M, the muscle; K, a keellike structure on basis capitulum; P, 
palpus; Si, Si, Ss, spines. 

2. Bird-infesting mites, living on or among the feathers; usually heavily 

sclerotized Analgesidae 

Mites not living on or among the feathers of birds; soft-bodied mites 3 

3. Parasitic on insects only Canestrimidae 



joo MEDICAL ENTOMOLOGY 

Parasitic in or on the living tissues of vertebrates 4 

4. Vulva longitudinal; parasitic in the skin and tissues of birds (mainly 

the air passages and air cells) Cytoleichidae 

Vulva transverse; parasitic in or on the skin of mammals and birds 

Sarcoptidae 

THE FAMILY SARCOPTIDAE 

Species of this family produce skin diseases of man and other animals known 
under such names as scabies, sarcoptic itch, "Norwegian itch," "barber's 
itch," psoroptic itch, acariasis, etc. The species are all skin-infesting and live 
primarily beneath the scabby incrustations that their activities induce. Certain 
species (Sarcoptes spp.) are burrowing in their habit and form tunnels below 
the surface of the skin. Though a considerable number of genera have been 
described in this family only a few of them are of interest here. These may be 
separated by the following key. 

KEY TO GENERA OF SARCOPTIDAE 

1. Suckers of the tarsi with segmented pedicels; males with anal suckers 

(Fig. 32 A) Psoroptes 

Pedicels of the suckers not segmented or suckers may be absent (Fig. 315) 

2 

2. Females with tarsal suckers lacking on all the legs; anal opening ter- 

minal; parasitic on birds Cnemidocoptes 

Females with tarsal suckers on some of the legs 3 

3. Tarsal suckers on all the legs of the male and on the first, second, and 

fourth of the female. (Species infest horses and cattle) Chorioptes 

Tarsal suckers not arranged as above; suckers on the first, second, and 
fourth pairs of legs of the male; on the first and second pairs of the 
female (Fig. 31 B) 4 

4. Anal opening on the dorsal surface; dorsal surface of the body with only 

short, sharp setae Notoedres 

Anal opening terminal or partially ventral; dorsal surface of the body 
with pointed scales and blunt, stout spines (Fig. 31 A) Sarcoptes 

THE GENUS SARCOPTES LATREILLE 1806: Sarcoptes contains those 
species that produce the true scabies or itch of man and animals. Whether 
there is only one species with numerous varieties or a number of distinct 
species attacking different animals is still a much-disputed question. Further- 
more, whether the various so-called species on different animals will attack 



THE ORDER ACARINA 101 

man has not been determined for many of them. It is preferable to follow the 
practice of recognizing only one valid species and listing as varieties or sub- 
species those found on different animals. The type species is Sarcoptes scabiei 
de Geer, found on man, though it is often written S. scabiei var. hominis 
(Hering). 
Sarcoptes scabiei :ft\\t human itch mite has been carefully studied by several 




Fig. 37. (A} and (#) Dorsal and ventral views o Sarcoptes scabiei. (C) Sarcoptes 
scabiei in its burrow in the skin. (D) Pcdiculoides ventricosus, mature female before the 
development of its young. () P. ventmcosus, female, showing the abdomen greatly 
swollen by the developing young (D and E not drawn to the same scale), a, anal opening; 
e, eggs in burrow; f, female at end of burrow; s, suckers. 

workers, especially in recent years. The adult female (Fig. 31) measures 
330 to 450 microns in length and 250 to 350 microns in width. The male is 
considerably smaller, a little more than half the size of the female. The dorsal 
surface of the body is marked with numerous parallel lines except in atf 
anterior median area; stout, blunt spines and irregular scales are prestnt and 
arranged as shown in Fig. 31. Several pairs of long and short hairs are also 
present. The number, arrangement, length, and shape of these structures seem 
to be of some systematic significance. The ventral surface is smooth except for 



102 MEDICAL ENTOMOLOGY 

a few hairs or bristles. The anterior two pairs of legs are widely separated from 
the posterior two pairs. The most striking structures are the epimeres or 
chitinous supports for the legs|(Fig. 31 B). The epimeres of the first pair of 
legs are united and form a narrow rod lying in the median line; those of the 
second pair do not unite but lie on either side of the body. The epimeres of the 
last two pairs of legs are not so prominent except in the male where they 
unite. The tarsal suckers consist of unsegmented pedicels and are present on 
the first and second pairs of legs of the female and on the first, second, and 
fourth of the male. 

LIFE CYCLE iiThis mite and its various subspecies excavate horizontal, tor- 
tuous tunnels in the upper epidermis, the horny layer (Fig. 31). In man these 
burrows are usually found on definite areas of the body, particularly between 
the fingers, wrists, elbows, axillae, region of the groin and external genital 
organs, back of the knees, ankles, and toes. In children all parts of the body 
may be infested; in women the undersides of the breasts are said to be favorite 
locations/According to Munro definite egg burrows are made by the mature 
female. She bores directly into the skin, becoming completely concealed in 
from a few minutes to nearly an hour. Burrowing usually continues, and 
2 to 5 mm. is excavated daily, fcgg laying commences with the burrowing and 
continues for about four to five weeks. The eggs are deposited directly behind 
the female (Fig. 31), and normally she deposits one or two eggs each day. The 
exact number of eggs laid by a single female has not been determined but 
probably 40 to 50 is about the average. The eggs hatch in from three to four 
days. The larvae leave the parent burrow and, passing to the surface of the 
skin, enter hair follicles or penetrate the skin between hairs; vesicles may form. 
The larval stage lasts from two to three days. The larva then molts in its 
burrow. There are two nymphal stages, the nymphs making narrow, shallow 
burrows. Mating takes place in the burrows^he males seeking out the females, 
though Mellanby (1943) thinks mating occurs on the surface of the skin, 
frhe fertilized female then proceeds to form an ovigerous burrow. The entire 
life cycle from egg to adult varies from 8 to 15 days. The adults live for three 
to five weeks. As the life cycle is comparatively brief, a mild infection may 
become marked in a short time.f According to Mellanby, it requires several 
weeks before an infection becomes apparent and requires medical attention. 
He has also shown that in man (some 900 cases) the average number of adult 
female mtfes per patient rarely exceeds fifty. However, many severe infesta- 
tions have been reported, and the number of mites must have been large or 
secondary infection (bacterial 1 ; occurred. 



THE ORDER ACARINA 103 

EFFECT ON HosTf The initial attack is without definite symptoms for the first 
few weeks. As the host becomes sensitized, the presence of the mites in the 
skin causes intense itching, especially at night when the warmth induces the 
mites to greater activity.'lncessant scratching follows, and the effects of the 
scratching may be more serious than the work of the mites. ftVhere the egg 
channels are formed and the larvae and nymphs burrow in the skin, small 
serous vesicles appear. Scratching ruptures these vesicles, and, on healing, 
minute crusts are formed. In severe infestations secondary complications may 
follow, such as infection with Streptococcus specieslDiagnosis of scabies must 
rest on finding the mites and the burrows in the skin. The mites are not present 
in the vesicles but usually close beside them at the end of linear, shallow bur- 
rows. As scabies may be masked or confounded with other skin diseases, it is 
essential that the mite be found before a final diagnosis is made. 
I Sarcoptic mites are not easily transferred by simple contact, though cases 
of such are on record. The most common methods are by close contact with 
infected persons, as by sleeping with them, by cohabitation, by using their 
clothing or bedding, or, among children, by playing and holding hands. 
Munro has shown that the cast-off clothing of infected persons remains capable 
of infecting others for at least n days if the clothing is moist; if the clothing is 
dry, infection dies out in two or three days.i During the First and Second 
World Wars there were severe outbreaks of sarcoptic itch in the various armies. 
These outbreaks, though marked among the troops, were also present in the 
general population of many countries. Mellanby (1943) states that in Great 
Britain the normal population showed an infection rate of about i per cent 
in 1939 anc ^ this increased to about 5 per cent in many parts of the country 
during the war. The average for the country as a whole was about 2 per cent. 
Women, especially young women, showed an incidence about twice as great 
as did males. 

TREATMENT: Persons infected with sarcoptic itch should obtain medical atten- 
tion. During the last world war several effective treatments were developed, and 
these proved easy of application. The American Army formula was known 
under the code name NBIN and consisted of the following compounds Ibenzyl 
benzoate 68 per cent; DDT 6 per cent; benzocaine 12 per centl'Tween 80, 
14 per cent (all by weight). For treatment the concentrate should be diluted 
at the rate of one part to five parts of water. Before applying treatment the 
infected person should take a hot bath, scrubbing the lesions vigorously with 
a tincture of green soap. The dilution may then be applied either by a sponge 
or as a spray, and the whole body should be carefully covered. The patient 



104 MEDICAL ENTOMOLOGY 

should not bathe for at least 24 hours.*|Many reliable proprietary brands are 
on the market as benzyl benzoate solutions, benzyl benzoate ointment, or 
other trade names. These are said to be very effective, and the patient should 
follow the directions of the manufacturer. One thorough treatment by these 
preparations usually gives complete cure, though it may be well to follow this 
by a second about a week later. ^The British formula as given by Mellanby 
(1943) is very easy to prepare and is said to be very easy on patients with 
tender and abraded skins. It is as follows: "Benzyl benzoate, 200 mils; Stearic 
acid, 20 gr.; Triethanolamine, 6 mils; water to produce 1000 mils. Heat the 
benzyl benzoate and stearic acid together until the latter is dissolved. Mix 
the triethanolamine with the water and then pour into the warm benzyl 
benzoate acid mixture and stir." This makes a good emulsion and is very easy 
on the skin. Other mixtures are also on the market but those with benzyl 
benzoate as the prime ingredient are preferred. Where these compounds can- 
not be obtained the sulphur ointment (10 to 15 per cent) may be used, but 
this requires at least three treatments morning and evening without bathing. 
Bathing should precede the first treatment and follow the last. In all cases the 
clothing and bedding of infected patients should be sterilized by laundering 
or by dry heat. 

JThe so-called "Norwegian itch" is caused by the same species of Sarcoptcs 
but oftentimes is marked by gigantic crusts due to long infestations. Another 
disease called "craw-craw" in parts of Africa is characterized by nodular and 
scabby dermatitis but has been shown to be caused by Sarcoptes.^ 

Other Sarcoptes: Itch mites have been described from many different mam- 
malian hosts. Over 18 to 20 different species or varieties are known, as S. equi 
(from the horse), S. cants (from the dog), S. ovis (from the sheep), S. suis 
(from the pig), and S. bovis (from the ox). Nearly all recent work indicates 
that these are not separable on morphological characters but appear as 
physiological races or varieties of the one species S. scabiei de Geer. If this is 
true, can man become infected by the animal-infesting forms? There are 
many records of man's becoming infected with some of these forms, especially 
by S. scabiei var. equi (by grooms and others attending infested horses), by 
var. caprae and var. ovis (by goat and sheep herders) . During a recent epidemic 
of scabies of cattle by S. scabiei var. bovis in the northeastern United States 
there were many reports of human infection, but so far as the writer is aware 
these infestations were of a temporary nature. 

THE GENUS PSOROPTES GERVAIS 1841: Species of Psoroptes are 
nonburrowing itch mites that possess tarsal suckers with jointed pedicels 



THE ORDER ACARINA 105 

(Fig. 32). Like Sarcoptes, rather numerous species of Psoroptes have been 
described from various animals. P. communis var. ovis (Hering) produces a 
serious disease of sheep, psoroptic itch or scab. The mite causes the wool to fall 
out or to mat together and severe scabby incrustations to form, and, in general, 
the infected animals present a scraggy and dilapidated appearance. This dis- 
ease is widespread in sheep-raising regions but can be controlled by the use 




Fig, 32. Left: A common nonburrowing itch mite, Psoroptes communis. Right: A 
hair-follicle mite, Demodex Jolliculorum. A, segmented pedicel o sucker. 

of appropriate dipping solutions. Other varieties are P. communis var. cqui, 
on horses; var. bovis, on cattle; var. cuniculi (Fig. 32), on rabbits. (This variety 
on rabbits seems to prefer the ears and, in laboratory animals, causes them to 
swell enormously. Frequently they penetrate deeply into the ear and cause 
death.) Many other varieties from different animals have been recognized. 

OTHER GENERA: Species of the genus Notocdrcs infest cats and rats. 
They are found principally about the ears, snout, tail, and anogenital region 
or among the fine hairs of the lower part of the legs. The itch produced is 



io6 MEDICAL ENTOMOLOGY 

rather severe. The species on cats or rats may also occur on man. Gordon et al. 
(1943) give an extended account of the habits and biology of this mite. 
Chorioptes equi causes a mange on the feet of horses and C. bovis produces a 
mange on cattle. Cnemidocoptes mutans affects fowls, causing a rather serious 
disease known as scaly leg; C. gallinae is found at the base of feathers and 
is known as the "depluming mite." 

THE TROMBIDOIDEA 

The Trombidoidea constitute a large group of mites that are mainly free- 
living, feeding on plant juicejs, or they are predaceous; some are parasitic while 
others are free-living in the nymphal and adult stages and parasitic in the larval 
stage. They are trarhenfe mjre.s. the spiracles located on or near the basesof the 
cheliccrae. The mouth parts are either prominent and raptorial or they are 
modified for piercing ancrsucking. The last segment of the palpus is modified 
into a thumblike structure capable of apposing the clawlike extension of the 
penultimate segment. The body is never strongly sclerotized, and chitinous 
plates are rarely present. , - 

This group is divided into a number of families, six or more. Only one 
family, the Tjjimhidiidae, is of interest here as it contains species that are fre- 
quently parasitic in the larval stages, oi\ man and other animals. Parasitic 
forms are known in some of the other families and a few have been reported 
as annoying to man, but they are of minor importance. This family is fre- 
quently divided into two subfamilies, the Trombidiinae and the Trombi- 
culinae. Recently Ewing (1944) has recognized these as distinct families. 
They may be separated by the following brief key : 

1. Abdomen of adults and nymphs strongly constricted somewhat in front 

of the middle; eyes, when present, never stalked. Eggs laid singly. 
Larvae parasitic on vertebrates Trombiculinae 

2. Abdomen of adults and nymphs not constricted; eyes usually present 

and frequently stalked. Eggs laid in clusters. Larvae parasitic on in- 
vertebrates Trombidiinae 

THE SUBFAMILY TROMBICULINAE 

To this subfamily belong the harvest mites, the chigger mitcs^and others that 
are parasitic on vertebrates during their larval stage and arc free-living in the 
nymphal and adult stages. Many of these mites are brilliantly colored red, 
scarlet, or spotted with variegated colors. They bear various names as "diig- 
gers," "harvest mites," "scrub mites," bete rouge, and rottget. Until recently 



THE ORDER ACARINA 107 

only a few genera were known, but at the present time some 26 genera and a 
large number of species have been described; many or most of them are from 
the Oriental and Australasian regions. Michener (1946) states that 13 genera 
are known from the Western hemisphere, and these include about 90 species. 
Of these 90 species only 8 are known as adults or have been reared to the 
adult stage. The species are based mainly on the larval state since very few 
(10 species) have been reared to the adult stage. The following^pecies are of 
interest because of their constant attacks on man or as vectors of important 
diseases. 




/ 



Fi^. 33. Eutrombicula alfreddugesii (Oudemans). Left: Larva (North American chig- 
ger), greatly enlarged. Right: Adult, a, abdomen; ae, anterior eye; as, anterolateral seta; 
dp, dorsal plate; hs, humeral seta; Is, lateral seta; ms, median seta; p, pseudostigma; 
pa, palpus, pc, palpal claw; pe, posterior eye; po, pseudostigmatic organ; ps, posterolateral 
seta. (From Manual of Tropical Medicine, courtesy W. B. Saunders; modified from 
Ewing.) 

Eutrombicula alfreddugesii (Oudemans) [Leptus irritans of literature] 
>is thc^common chigger (Fig. 33) that aj^acks mnn in North America. It is 
generally distributed from New York to Minnesota, southward to the Gulf 
of Mexico and in Mexico. In the southern states it is^ery prevalent during the 
summer months^ and its attacks are very annoying. The larval mites are very 
minute and easily penetrate the clothing. They attach by means of their hooked 
chelicerae and armed palpi. The method of feeding is very interesting. The 
chelicerae are inserted in the skin, frequently about a hair follicle and usually 



io8 MEDICAL ENTOMOLOGY 

under or near clothing where there is pressure. The mite then injects into the 
tissues a fluid that has a remarkable effect. This fluid liquefies the immediate 
tissues, but the surrounding tissues become hardened and form a tube, fre- 
quently referred to as the stylostome or hypostome (Fig. 34). The liquefied 
tissues are ingested by the mite, and as feeding continues the tube becomes 
lengthened as more of the tissues are dissolved. The stylostome may become 
as long as the mite, and when the mite releases its hold this tube is left in the 
tissues. The effect of the digestive juices is to cause severe itching followed 

by a marked dermatitis. Incessant scratch- 
ing may bring about secondary infection, 
and the result may be dangerous. After 
feeding, the larval mites drop to the 
ground and later molt to the eight-legged 
nymphal stage. The nymphs are not 
parasitic and probably feed on vegetable 
matter. This is also true of the adults. 
The females deposit their eggs singly on 
the ground.lHow many generations de- 
velop in a summer season does not seem 
to be known /In the larval stage this mite 
attacks all sorts of vertebrates as rabbits, 
Fig. 34. A diagrammatic illustration mice, rats, snakes, turtles, poultry, and 
of the formation of the stylostome by a qua il. /Jenkins (1947) gives a concise ac- 
Ncoschongastia sp. in the ear of a rat. r , c 

Ch, chelicerae of mite; Sty, stylostome. count of reann S several generations of 

this mite and also of E. masoni. He reared 

the nymphs in soil in jars, feeding them on the eggs of mosquitoes (Aedes 
aegypti) . At the present time this mite is not known to transmit any human 
disease. 

Eutrombicula batatas (Linn.), known as the "patatta" mite of Surirlam, 
occurs from Surinam to Panama, /north to Puerto Rico, Florida, Alabama, 
and parts of Mexico. According to Michener (1946), the adults are found in 
open sunlight areas among short grass. The females lay their eggs on the 
ground. The eggs hatch in four to five days into what has been called the 
"deutovum" stage of mites (the eggshell bursting and showing a quiescent 
undeveloped larva, Fig. 35). This stage lasts six to seven days, and from it 
emerges an active, six-legged, reddish larv g a. The larvae occur on the grass or 
weeds, often in great numbers, especially about houses where domestic ani- 
mals such as chickens are numerous. The larvae readily attach to man, 
domestic animals, rats, or birds. On man they seem to settle mostly in the 





Fig. 35. A chigger mite, Eutrombicula batatas (Linn.), (a) Dorsal 
view of adult. () Dorsal view of nymph. (<r) Dorsal view of larva. 
(J) Lateral view of deutovum. (<?) The egg. (All to the same scale; 
After Michcner, Annals oj the Entomological Society oj America?) 



j io MEDICAL ENTOMOLOGY 

groin region, under the armpits, under the belt line, or on the ankles under 
the socks. They remain attached for three to six days and then drop from their 
hosts. Within the larval skin the protonymph appears, and later the first 
nymphal stage emerges from the larval and protonymph integuments in six 
or seven days after the larva dropped from its host. The eight-legged, dull-red 
nymph Jnnks like the adult except in size. The nymphs remain on the ground, 
but their exact food was not determined. In about two weeks or longer the 
nymphs become quiescent and in about a week transform to adults. The 
adults have been kept alive for at least 45 days. Though the exact food of 
the nymphs and adults was not determined, Michener suggests that they live 
on the soil moisture rich in organic matter as they possess sucking mouth parts. 
This species is not known to transmit any disease. 

Trombicula autumnalis (Shaw) is a very troublesome mite in various parts 
of Europe. It is a pest not only of man but of horses, cattle, dogs, cats, and 
rabbits. According to Fuss and Hansen (1933), it produces on man a severe 
dermatitis with inflammation, necrosis of the epidermis, and hyperemia. The 
itching is intense. 

Trombicula a\amushi (Brumpt) occurs over extensive areas of Japan, For- 
mosa, parts of Korea, and the Pescadores, and it is reported from the Malay 
Peninsula. This species is of great importance as it is known to be the vector 
of Japanese river fever, tsutsugamushi disease, or, as it is frequently called, 
kedani fever. The life history of this mite and its relation to tsutsugamushi dis- 
ease were rather fully elaborated by Japanese workers between 1900 and 1918. 
In World War II tsutsugamushi disease appeared among American and Al- 
lied troops in various parts of the South Pacific and Burma theaters of opera- 
tions. As a result extensive and intensive investigations have been carried on 
and much new data obtained. 

T. afymushi (Fig. 36), like other mites parasitic in the larval stage, not only 
feeds on man but attacks mice, rats, and other rodents. It is especially fond of 
the voles (Microtus montebelli in Japan) in the ears of which it seems to 
congregate. The period of larval attachment is three to four days. The method 
of feeding is similar to that of Eutrombicula aljreddugesii. (This is believed 
to be true of all the parasitic larval mites of the subfamily Trombiculinae.) 
Leaving the host the larvae seek shelter in the ground, where they transform 
to nymphs in from two to three weeks. The nymphs are said to feed only on 
plant juices or decaying organic matter. The nymphal period lasts some three 
to ten or more weeks (no very accurate data seem to be available 6n the activi- 
ties and length of the nymphal life) . The adults live on the ground and are 
said to feed on plant juices. They are known to hibernate during the winter 



THE ORDER ACARINA 



in Japan. In the spring the females deposit their eggs singly on the ground 
under trash or other covering. Unfortunately very few new data have been 
obtained on the life cycles, habits, or biology of the various species of mites 
occurring in the regions where kedani fever is now known to be prevalent. 




Fig. 36. Larva of Trombicula aJ(amushi. A, abdomen; Ae> anterior eye; As, anterolateral 
seta; Bes, basal segment of chelicera; Ds, dorsal shield or plate; Gs, branched galeal seta; 
H, one of the dorsal hairs; Hs, humeral seta; Ms, median seta; P, pseudostigma; Pa, pal- 
pus; PC, palpal claw; Pe, posterior eye; Po, pseudostigmatic organ; Ps, posterolateral seta. 
(Modified from Hirst.) 

Trombicula deliensis Walch was described from Sumatra. It is distributed 
in many parts of Malaya, northern India (Simla Hills), the East Indies, 
northern Australia, and probably in other parts of southeastern Asia. It occurs 
on various species of rats and other rodents and readily attacks man. 

Trombicula fletcheri Womersley and Heaslip was described in 1943. It 



H2 MEDICAL ENTOMOLOGY 

is found commonly in the New Guinea area and readily attacks man. It is a 
common parasite of rats and bandicoots and is recorded from several other 
hosts. Little seems to be known of its life history, and its distribution is, as 
yet, not fully known. Trombicula walchi was described by Womersley and 
Heaslip from the New Guinea area, but many authorities seem to think it is 
the same as T. deliensis. 

Many other species of Trombicula and related genera have been described 
from the southwest Pacific area, but little is known about their biology or 
distribution. Trombicula hirsti Sambon is generally called the "scrub mite" 
of parts of Australia; T. wichmanni Oudemans, is said to be a pest in the 
Celebes and New Guinea; Leeutvenhoetya australiensis Hirst is troublesome 
in New South Wales. 

CONTROL OF MITES: Very effective mite repellents were developed 
during the recent world war. Briefly these are: 

(1) Dimethyl phthalate or dibutyl phthalate used as liquids on all openings 
of the clothing. These are applied by hand or the entire clothing can be 
sprayed. In using them apply liberally along all openings and especially about 
the socks and edges of trousers. These materials can also be used to impreg- 
nate clothing. These solutions can be purchased and the directions of the 
manufacturer should be followed. 

(2) Benzyl benzoate as developed in the NBIN formula for the control 
of sarcoptic itch mites is also effective (see pp. 103-104). Clothing is impreg- 
nated with this mixture and it withstands several launderings or even longer. 

(3) Benzyl benzoate alone also gives excellent repellent effect when cloth- 
ing is impregnated with it. The repellent effect persists even after four or five 
launderings. 

(4) Other repellents have been tested but not sufficiently to warrant their 
use at the present time, 

TROMBICULID MITES AND DISEASE: The attacks of various species 
of mites throughout the world usually result, in man, in a marked dermatitis 
accompanied by intense itching. The scratching of the areas may induce sec- 
ondary infections that may be serious. However, it is as vectors of disease that 
certain species are dangerous. 

Tsutsugamushi disease was recognized in man in Japan as early as 1878, 
and Baelz and Kawakami (1879) published on account of what they described 
as "Japanese river fever." The disease was confined to overflow areas of certain 
river valleys. The natives associated it with the bite of a red mite (akamushi). 
Japanese workers, between 1893 and 1918, fully established that the mite, 



THE ORDER ACARINA 113 

Trombicula akamushi, was the vector of the disease; that rodents, principally 
the vole, Microtus montebelli, were the reservoir; and that the virus is .passed 
through the egg to the young of the infected mites. They also described the 
life cycle of the mite and largely determined its distribution in Japan and 
Formosa. In 1930 Nagayo and his associates discovered the etiological agent 
and named it Ric^ettsia orientalis. It is now well established that the reservoir 
of this disease is in rats, mice, voles, and other rodents; the mites obtain the 
rickettsiae while feeding on infected hosts, and these are passed through the 
nymphal stage to the adults and by the adults through the eggs. Larvae from 
infected mothers then transmit the disease to man when they feed on him. 
The point of feeding by infected larvae usually shows a distinct scar (eschar) . 
The incubation period in man is 7 to 10 days or may be prolonged to 14 days. 
The mortality rates vary, but range from 60 per cent for older persons to 15 
per cent for the n- to 20-year age group in Japan. Blake et al. (1946) give an 
over-all death rate of 30 per cent in Japan. Throughout southeast Asia, the 
islands of the southwest Pacific, and Australia various typhuslike diseases have 
been described such as Mossman fever from Australia, scrub typhus from 
Malaya, pseudotyphus from Sumatra, endemic typhus from India, and tropical 
typhus from Indo-China. During World War II these diseases were investi- 
gated by a large number of workers with the result that all these diseases were 
declared to be manifestations of tsutsugamushi disease. At present this disease 
occurs in India, Ceylon, Burma, Indo-China, Malaya, Sumatra, Java, Borneo, 
Celebes, New Guinea, northeast Australia, New Britain, Bougainville, parts 
of the Philippines, Formosa, Japan, Korea, and probably parts of China. The 
vectors are Trombicula a\amushi, T. deliensis, T. fletcheri, T. walchi 
( deliensis), and probably others. The reservoirs of Ricftettsia orientalis are 
in voles (especially Microtus montebelli in Japan), in wild rats of various 
species, and in other rodents. McCulloch (1944, 1946) reports Schongastia 
blestowei and Trombicula wichmanni as probable vectors on epidemiological 
evidence. 

THE TARSONEMOIDEA 

This superfamily includes a large number of mites that are primarily plant- 
inhabiting or that infest foods of various kinds. A few species are known to 
be parasitic, and one species, under certain conditions, may attack man. 
Acarapis woodi Rennie lives in the tracheae of honeybees and produces a 
serious disease of the adults known as "Isle of Wight disease." Two species 
have been recorded as invading the tracheae of grasshoppers (Wehrle and 
Welch, 1925). 



ii 4 MEDICAL ENTOMOLOGY 

Pediculoides ventricosus Newport, the grain itch mite, is a predaceous mite 
(Fig; 31) that feeds on the larvae of various insects infesting seeds, grains, 
plants, or their products. It feeds on the larvae of the Angoumois grain moth 
(Sitrotroga cerealella Oliv.), the pink bollworm of cotton (Pectinophora 
gossypiella Saunders), the joint worms (Isosoma grande Riley and /. tritici 
Fitch), the bean and pea weevils (Mylabris quadrimaculatus Fabr. and M. 
obtectus Say), and others. There is marked sexual dimorphism in this mite 
(Fig. 31). The abdomen of the fertilized female becomes greatly swollen as 




Fig. 37. Lesions produced on man by the 
bites of Pediculoides ventricosus. (After 
Webster.) 



F:g. 38. Demodex cants. Base of a seba- 
ceous gland of a dog packed with Demo- 
dex canis. 



the eggs hatch within the body of the mother, and the young are retained till 
they reach sexual maturity. A single female may give birth to as many as 270 
sexually mature mites. In seeds, grain, straw, cotton, beans, or other plant 
material infested with the insect larvae noted above, this mite may occur in 
enormous numbers. Man is attacked when handling such infested material 
or sleeping on infested straw, or when he in other ways comes in contact with 
large numbers of the mites. On man their bites produce a rashlike dermatitis, 
which may cover the entire body (Fig. 37). The rash appears 12 to 16 hours 
after the attack and consists of wheals and papules of varying size. Vesicles or 
pustules may develop, and the attacked areas may become very red and have 



THE ORDER ACARINA 115 

a burning, itching sensation. Fever and sweating are recorded as concomitants 
in some cases. Ciarrocchi (1928) describes an epidemic of pruriginous derma- 
titis in Italy caused by this mite. Its attacks have been recorded from widely 
scattered regions of the world. Diagnosis of this rash must be based on the 
occupation or sleeping habits of the patient and the discovery of the mites. 
Treatment consists of avoiding further infestation; recovery will be rapid. In 
severe cases the rash may be reduced by bathing in warm, soapy water, fol- 
lowed by the application of a mild talcum powder. 

THE TYROGLYPHOIDEA 

The mites belonging to this superfamily are minute and abound on dried 
fruits, other foodstuffs, roots, and bulbs. Man becomes infested from handling 
infested products. Vanilla pods and beans are often heavily infested, and a 
dermatitis, known as "vanillism," frequently occurs among vanilla workers. 
It is believed to be caused by the mite Tyroglyphns siro Linn. Copra itch 
is a common dermatitis among workers in the copra mills and was first de- 
scribed by Castellani in Ceylon. It is caused by Tyroglyphus longior var. castel- 
lani Hirst. This dermatitis may affect copra workers in all parts of the world. 
A so : called "grocers' itch" is caused by Glyciphagus prunorum Hermann 
(G. domesticus de Geer), which often abounds in grocery stores. The derma- 
titis caused by these mites may be mistaken for scabies or other types of skin 
diseases. For the purpose of diagnosis the history of the patient's work may 
often give a clue to the causative agent. Treatment consists of various oint- 
ments and the avoidance of mite-infested plants or foodstuffs. 

As mites of this family abound in foodstuffs, they have been recorded many 
times from fecal examinations. Whether they cause any trouble in the in- 
testinal tract does not seem to be known. Mekie (1926) has reported the 
infection of the urinary tract by three species, Tarsonemus floricolus C. and F., 
Glyciphagus domesticus de Geer, and Tyroglyphus longior Gerv. He also re- 
viewed previously reported cases. Hinman et al. (1934) reported a case of 
intestinal myiasis due to Tyroglyphus longior Gerv. It is difficult to conjecture 
how such infection takes place except through uncleanly habits. 

THE DEMODICOIDEA 

The Demodicoidea, the hair-follicle mites, are a highly aberrant group of 
mites. They are parasitic in the hair follicles and sebaceous glands of mammals. 
They are very elongate (Fig. 32), the legs are reduced to mere stumps, the 
abdomen is vermiform, and the mouth parts are modified, minute, and fitted 



n6 MEDICAL ENTOMOLOGY 

for piercing. The superfamily contains but a single family, the Demodicidae, 
and one genus, Demodex. The hair-follicle mites of different animals are ex- 
tremely difficult, if not impossible, to differentiate as distinct species. Hirst 
(1919) has brought more or less order out of the chaos and has redefined the 
various forms. 

Demodex jolliculorum Simon is the hair-follicle mite of man. It is abundant 
in some countries, but it is said to be rare in North America. It lives deep down 
in the hair follicles and sebaceous glands. The entire life cycle is passed on 
the host so that the infection gradually spreads. It is not considered of any 
pathogenic importance to man. 

Demodex can is Ley dig (Figs. 38,39) attacks dogs and is cosmopolitan in 
distribution. It causes the follicular or red mange of the dog. The disease is 
serious and there is no known successful treatment. D. cati Megnin parasitizes 
the cat; D. bovis Stiles, cattle; D. equi Raillet, horses. Other species are found 




Fig. 59. A gland from a dog, showing Demodex cams along the entire gland. 

on different mammals. Baker (1946) reports a serious infection of a cow with 
demodectic mange. The mange appeared as enlarged nodules, and each 
nodule when opened contained an enormous mass of the mites in all stages. 
This type of mange is apparently very rare. Several workers have recorded 
D. canis parasitizing man, but Hirst regards these cases as doubtful. 

THE CLASS PENTASTOMIDA 

The tongue worms and their allies 

This aberrant group has had a varied taxonomic career, having been placed, 
at one time or another, with the Cestoda, Nematoda, and Hirudinea. Van 
Beneden (1848) placed it in the Arthropoda, and Sambon (1922) established 
its position as in the Acarina though now it is regarded as a distinct class. 

The adults are elongate, legless, cylindrical, or flattened worms divided 
externally by conspicuous rings that are not true segments. The mouth is 
provided with a chitinous armature, which is located before, behind, or be- 
tween two pairs of hollow, retractile, fanglike hooks (Figs. 40,41). The sexes 



THE ORDER ACARINA 



117 



are distinct, the males smaller than the females. There is no separation of the 
head, thorax, or abdomen. Anteriorly the most conspicuous features are the 
hollow fangs or retractile hooks. At their bases open a number of glands, the 
secretion of which is supposed to have a hemolytic action. The internal struc- 
ture is very simple. The mouth opens into a pharynx, which connects with a 
short esophagus. The pharynx is supplied with muscles, which undoubtedly . 




Fig. 40. (/) Armillifer armillatus, female. (2) Male. (Both drawn to the same scale.) 
(3) Head of A . armillatus to show the fangs. (4) Nymphal stage of same species in liver. 
(5) Recently hatched larva of same species. (6) Fully developed embryo within the egg 
of Poroccphalus subulijer. (All modified from Sambon.) 

serve to exert a sucking action. The esophagus opens into the mid-gut or 
stomach, which is somewhat capacious and extends the entire length of the 
body to the rectum. There is no trace of circulatory or respiratory organs. The 
nervous system is vestigial. The main organs appear to be for reproductive 
purposes as the ovaries and testes are well developed. In the females the 
opening of the vagina is either at the anterior or posterior end of the body. 

Hey mans and Vitzthum (1936) in an extensive paper divide the Pentasto- 
mida into two orders, which may be separated by the following scheme: 



1 1.8- MEDICAL ENTOMOLOGY 

1. Hooks located on fingerlike processes or slight swellings of the body back 

of the mouth ; genital opening anterior in both sexes 

Order Cephalobaenida 

Two families: Cephalobaenidae (in lungs of snakes and lizards); 

Reighardiidae (in air sacs of birds) 2 

2. Hooks not so located but arranged on each side of the mouth either 

in a straight, curved, or arched line; genital opening of the female 

posterior Order Porocephalida 

Two families: Porocephalidae (body cylindrical; adults in lungs of 
reptiles; young in a great variety of vertebrates including man); 
Linguatulidae (body flattened; adults in nasal passages of dog and 
cat family; young in all sorts of mammals including man) 

As far as known all species of this class have a complicated life cycle, the 
larval and nymphal stages in one host and the adults in another. Linguatula 
serrata occurs in the adult stage in the nasal passages and frontal sinuses of 
dogs (occasionally in man and some herbivores), where they suck blood. They 
cause a severe catarrh, suppuration, and bleeding. The eggs of the parasite are 
discharged in the mucus and wastes from the nostrils, infecting water or 
vegetation. If these eggs are eaten by rabbits, sheep, goats, etc., or by man, the 
larvae escape from the eggs, migrate through the intestinal walls, and usually 
locate in the liver, or other organs where the nymphal development takes place. 
In a short time the larva (Fig. 40) becomes encapsulated by the host-tissue 
reaction and nymphal development proceeds. In about five or six months the 
nymphs become mature; they then possess two pairs of hooks and measure 
4 to 6 mm. in length. The body is divided into numerous rings, each bordered 
posteriorly by a row of closely set spines. Within the cysts the nymphs may 
live at least two or three years. If, however, raw liver or other organs con- 
taining these nymphs are eaten by dogs or man, the nymphs gain access to 
the nasal passages via the mouth or esophagus and there reach maturity. In 
Europe dogs are frequently parasitized and humans not uncommonly harbor 
the nymphs in their internal organs. Hobmaier and Hobmaier (1940) give 
a clear account of the life cycle of Linguatula rhinaria, a parasite of brown 
rats and dogs. Their account differs in many details from the records of other 
workers. 

In Africa man is frequently parasitized by Armillijer armillatus (Fig. 40) . 
This species is found as a mature parasite in pythons and other snakes; its inter- 
mediate hosts are primarily monkeys and apes, although carnivores and other 
animals have also been reported as infected. The natives of certain parts of 



THE ORDER ACARINA 1^9 

Africa regard python steaks as delicacies, and as a result frequently become 
infected by eating raw meat. Infection may also take place by eating raw vege- 
tables or drinking water contaminated with the eggs of the parasite. Human 
infection is common in many parts of West Africa, the nymphs being recovered 
at autopsies. Cannon (1942) reports the death of an African woman due to an 
extremely heavy infection of the colon by encysted nymphs of this species. 
A. moniliformis is parasitic in the respiratory tract of pythons, and records 
of human infections are rather rare (three so far recorded, one from Manila, 
one from Sumatra, and one from a Tibetan in China). 




Fig. 41, Porocephalus clavattis. Mature female from the lung cavity of a South Ameri- 
can snake. The central figure shows the head with the four characteristic fangs. 

Porocephaliasis is the usual term employed to designate human infection 
with species of Pentastomida. Sambon in 1910 and 1915 summarized the 
known human cases up to that time. It appears that when few nymphs are 
present in man the ill effects are not serious; when large numbers occur the 
effects may be dangerous, but there is no method of diagnosing their presence. 
Most of the present information of human infections is based on findings at 
autopsies or from abdominal operations. 

In America two cases of porocephaliasis are on record. As no species of 
Armillifer are known from the Americas, it is thought the infections may 
have been due to the nymphal stage of Porocephalus crotali of rattlesnakes 
or an allied form. Penn (1942) reports P. crotali as being found commonly in 
the larval and nymphal stages in muskrats (Ondatra zibethica rivalled) in 



120 MEDICAL ENTOMOLOGY 

Louisiana and the adults in the water moccasin (Agfystrodon piscivorui) . The 
adults live in the lung cavities of the snakes and the eggs are discharged in the 
sputum. When the infected sputum is eaten by the muskrat, the eggs hatch 
in the small intestine and the larvae migrate to the liver and lungs, where they 
become encapsulated in the tissues. The nymphs become mature in about 
three months. When infective muskrats are eaten by the water moccasin the 
nymphs migrate up the esophagus and into the tracheae and lungs, where 
they develop to adults. 

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THE ORDER ACARINA 123 

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culidae) in the western Pacific area. Jl. Parasit., 32: 286-322, 1946. 

Willcocks, F. C. The predacious mite, Pediculoides ventricosus Newpt. Agr. 
Jl. of Egypt, 4: 31-51, 1914. 

Williams, R. W. A contribution to our knowledge of the bionomics of the com- 
mon North American chigger, Eutrombicula aljreddugesii (Oudemans) with a 
description of a rapid method of collection. Amer. Jl. Trop. Med., 26: 243-250, 
1946, 



124 MEDICAL ENTOMOLOGY 

Womersley, H. A revision of the Australian Trombidiidae. Rec. S. Australia 

Mus., 6: 74-100, 1937. 
. Further notes on the Australian Trombidiidae with description of new 

species. Trans. Roy. Soc. S. Australia, 63: 149-166, 1939. 
. A revision of the Microtrombidiinae (Acarina, Trombidiidae) of Australia 

and New Guinea. Rec. S. Australian Mus., 8: 293-355, 1945. 
, and Heaslip, W. G. The Trombiculinae (Acarina) or itch mites of the 

Austro-Malayan and Oriental regions. Trans. Roy. Soc. S. Australia, 67: 

68-142, 1943. 
, and Heaslip, W. G. Notes on and additions to the Trombiculinae and 

Leeuwenhoekiinae (Acarina) of Australia and New Guinea. Ibid., 68: 82, 1944. 

CLASS PENTASTOMIDA 

Cannon, D. A. Linguatulid infestation of man. Ann. Trop. Med. Parasit., 36: 

160-167, J 94 2 - 
Darling, S. T., and Clark, H. C. Linguatula serrata (larva) in a native Central 

American. Arch. Internal Med., 9: 401-405, 1912. 
Faust, E. C. Linguatulidae (order, Acarina) from man and other hosts in China. 

Amer. Jl. Trop. Med., 7: 311-325, 1927. 
Heymons, R., and Vitzthum, H. G. Beitrage zur Systematik der Pentastomiden. 

Zeit. Parasitenk., 8: 1-103, 1936. 
Hobmaier, A., and Hobmaier, M. On the life -cycle of Linguatula rhinaria. 

Amer. Jl. Trop. Med., 20: 199-210, 1940. 
Noc, F. Sur 1'embryon acariforme et les stades larvaires des Linguatulides. Bull. 

Soc. Path. Exot., 16: 340-346, 1923. 
Penn, G. H. The life history of Porocephalus crotali, a parasite of the Louisiana 

muskrat. Jl. Parasit., 28: 277-283, 1942. 
Sagredo, N. Linguatula rhinaria (Pentastoma denticulatum) in den Lungen des 

Menschen. Virchow's Arch. Path. Anat. Physiol., 251: 608-615, J 924- 
Sambon, L. W. Porocephaliasis in man. Jl. Trop. Med. and Hyg., 13: 17-24, 

212-217, 258-262, 1910; 15: 321-327, 371-374, 1912; 16: 97-100, 1913. 

. A synopsis of the family Linguatulidae. Ibid., 25: 188-206, 391-428, 1922. 

Southwell, T. On a collection of Linguatulidae in the Liverpool School of Tropical 

Medicine. Ann. Trop. Med. Parasit., 18: 515-531, 1924 



CHAPTER V 



The Hexapoda: Insects 



^ I ^HE class Hexapoda contains an enormous assemblage of species, every- 
J-. where present and always abundant in all regions of the world. They 
are small animals possessing a body made up of transverse segments; their seg- 
ments are grouped into three distinct regions, the head, thorax, and abdomen. 
The segmentation shows most distinctly in the abdomen and thorax, whereas 
in the head the segments have become fused, forming a highly chitinized box. 
The number of segments is generally stated as twenty. These are distributed 
as follows: 6 constitute the head, 3 compose the thorax, and u form the 
abdomen. Typically each segment of the primitive arthropod bore a pair of 
appendages, but in insects many of these have been lost. There are readily 
visible but three pairs, the legs, which are attached to the segments of the 
thorax. The other appendages have been lost (as in the abdomen) or modified 
for other purposes (as the mouth parts, antennae, eyes, and external genital 
appendages). In addition, the great majority of insects possess a pair or two 
pairs of wings attached to the dorsolateral angles of the second and third 
thoracic segments. Insects breathe by means of a highly complicated system of 
tracheae, which penetrate every portion of the body and open externally by 
special orifices, the spiracles, situated at the sides of the body. 

The animals, as characterized above, constitute a vast assemblage, number- 
ing nearly a million described species. They far outnumber, in species, all 
other animals combined, while in individuals their vast multitudes are like 
the sands of the sea uncountable. Who can estimate the ants of a single 
hillside, the aphids of an orchard, or the flies of a city ? As a group, insects are 
considered to be the most successful of all forms of terrestrial animal life, yet 
man treats them with scant respect. 

EXTERNAL ANATOMY 

Externally the body of an insect is composed of transverse segments (20), 
which may or may not bear appendages. These segments are grouped into 



i 2 6 MEDICAL ENTOMOLOGY 

three regions, head, thorax, and abdomen (Fig. 42). The surface layer of 
the body is called the body wall or integument. It is more or less rigid and 
forms the skeleton within which all the organs and fleshy parts are enclosed; 
but the external covering is flexible along certain transverse and longitudinal 
lines and at other points, thus permitting a great variety of movements. The 
hardened portion of the body wall is due to the deposition of various substances 
in the chitin and it is variously distributed; usually lines (sutures) delimit 
the sclerotized areas, which are called sclerites. The arrangement of sclerites 
and their separating sutures constitutes the major feature of the external 
anatomy of insects. 




Fig. 42. Lateral view of a grasshopper to illustrate the principal external structures of an 
insect. (Wings of one side removed.) Ant, antenna; Cx, coxa; E, compound eye; F, femur; 
O, ocellus; Ovi, ovipositor; PN, pronotum; Sp, spiracles; Tar, tarsus; Tb, tibia; Tn, tym- 
panum of ear; Tr, trochanter; W, wing. 

THE BODY WALL 

The body wall is a continuous structure, and the apparent segmentation is 
due to infoldings. It completely surrounds the insect. It also extends internally 
and forms the lining of the fore and hind intestine; the tracheae are only 
invaginations of the body wall. The only external openings are the mouth, the 
anus, the spiracles, and those of the genital organs. The body wall is composed 
of a single layer of epidermal cells supported on a noncellular membrane 
(basement membrane). Outside these cells lies the cuticula, a product of the 
epidermal cells (Fig. 43). The cuticula may be soft and pliable, but it is usually 
sclerotized into definite areas, the sclerites. The cuticula is not a homogeneous 
structure. It is stratified into two primary layers, the endocuticula and the 



THE HEXAPODA: INSECTS 127 

exocuticula, and externally it is protected by a very thin layer called the 
epicuticula (Fig. 43). The two primary layers are composed mainly of chitin, 
whereas the epicuticula is nonchitinous. Chitin is a soft, pliable substance that 
is insoluble in water, alcohol, ether, dilute acids, or alkalies. It becomes hard- 
ened by the deposition of various substances, mainly in the exocuticula. The 
epicuticula is very thin and is largely impermeable to water. Most of the 
pigments are found in the exocuticula. The body wall is rarely smooth 
externally. On it are small spicules, hairs, spines, ridges, scales, setae, or other 
excrescences. Many of these are merely projections of the cuticula; others, such 
as stout spines, glandular hairs, and sense hairs, take their origin from the 
underlying epidermis. 




Tr 



Bm 



Fig. 43. Left: Diagrammatic longitudinal section of the body wall of an insect. 
Right: More enlarged and detailed sketch of a portion of a body wall to show 
structure. Bm, basement membrane; C, sclerotized portion of wall of segment; 
En, endocuticula; Ep, epicuticula; Ex, exocuticula; Hp, Hypodermis or epi- 
thelial cells; S, seta; T, the nonsclerotized part of body wall between two seg- 
ments; Tr, a trichogen cell. 

Each segment of the body is composed of a dorsal, lateral, and ventral area. 
In each of these areas definite parts, sclerites, may occur, and these are separated 
by sutures. These sclerites bear names, and the terminology becomes quite 
complex in some of the highly specialized insects. In general, there are recog- 
nized for each segment a dorsal sclerite, the tergum or notum; two lateral 
sclerites, the pleurites; and a ventral sclerite, the sternum. Each of these may 
be divided into a number of smaller sclerites. 



THE HEAD 

The head is composed of a number of fused segments (usually regarded 
as six), and these are so intimately consolidated as to form a hard case, the 



I 2 8 MEDICAL ENTOMOLOGY 

head capsule. Externally several distinct head sclerites may be recognized, 
especially in the more generalized insects. Some of these are delimited by 
sutures, but most of them are fused so that the names refer to areas rather 
than distinct sclerites. Fig. 42 will illustrate the structure as found in a gen- 
eralized insect and the terms employed. The main sclerites are the two that 
form the vertex (Fig. 44); the front or frons, an unpaired sclerite lying in 
front of the arms of the epicranial suture; the clypeus, a simple sclerite attached 
to the anterior margin of the front and usually fused with it; the labrum, a 
flaplike structure attached to the clypeus (this structure is usually included 
with the mouth parts though it is strictly part of the head capsule) ; and the 
genae, paired structures located below and somewhat behind the eye. That 
portion of the head behind the vertex and the dorsal or posterior surface is 
known as the occiput. In the more specialized insects the sclerites listed above 
become fused or modified, but in general the areas are designated by the 
names indicated. 

The Appendages of the Head 

The six segments that form the head have not lost all their primitive 
appendages though they have become highly modified and perform dif- 
ferent functions. The appendages still present in the adult consist of the 
following: (i) a pair of compound eyes, modified appendages of the first 
head segment; (2) a pair of antennae, which arise from segment two; (3) a 
pair of mandibles, appendages of segment four; (4) a pair of maxillae, ap- 
pendages of segment five; (5) a pair of appendages that unite to form the 
labium, the second maxillae of authors, appendages of segment six. The 
appendages of segment three are lost in the adult insect though vestiges of 
them are present in the embryo. The modified head appendages thus consist 
of eyes, antennae, and mouth parts. 

THE MOUTH PARTS : The mouth parts of insects may be quite simple, 
as in the grasshopper (Fig. 45), or they may be very complicated, as in the 
bloodsucking insects (Fig. 79) and the muscoid flies (Fig. 47) . In general, three 
types of mouth parts may be recognized, the mandibulate type, the piercing 
and sucking type, and the nonpiercing and sucking type. There are, of course, 
many modifications of these types. 

The Mandibulate Type (Fig. 45) : In this type the mouth parts consist of a 
labrum, a movable flap attached to the clypeus and overlying the upper margin 
of the mouth; a pair of mandibles lying directly below the labrum and moving 
laterally; a pair of maxillae arising below the mandibles and of rather com- 



THE HEXAPODA: INSECTS 
cs Y FS o 



129 




Fig. 44, (a) Frontal view of the head of a grasshopper (Mclanoplus sp.). () Lateral 
view of the head of a grasshopper, (c) Posterior view of the head of a grasshopper 
(Romalca sp.). (d) Sectional view of head of grasshopper to show the internal structures 
(d modified from Snodgrass). Ant, antenna; Ap, point of invagination for the anterior 
arm of the tentorium; At, anterior arm of tentorium; Cb, cibarium; Clp, clypeus; Cls, 
clypeal or epistomal suture; Cr, crop; Cs, coronal suture; Csl, cervical sclerites; Cx, con- 
dyles of the mandible; Da, dorsal arm of tentorium; E, eye; Fr, foramen magnum; 
Fs, frontal suture; Ft, front or frons; Ge, gena; Hphy, hypopharynx; Lb, labium; LbPlp, 
labial palpi; Lm, labrum; M, mentum of labium; md, mandible; MO, mouth opening; 
MX, maxilla; MxPlp, maxillary palpi; O, ocelli; Oc, occipital sclerite; Ocs, occipital suture; 
Pa, posterior arm of tentorium; Pge, postgena; Ph, pharynx; Pt, point of invagination of 
posterior arm of tentorium; R, genal suture or ridge; S, submentum of labium; SD, sali- 
vary duct; T, tentorium with its arms; V, vertex. 



i^o MEDICAL ENTOMOLOGY 

plicated structure; and a labium, closing the lower surface of the mouth and 
formed by the fusion of a pair of appendages (the second maxillae). On the 
under surface of the labrum and forming the roof of the mouth is a fleshy 
organ known as the epipharynx (Fig. 45) . It is supplied with sense hairs and 
is supposed to function as an organ of taste. This structure becomes highly 
developed in many sucking insects and serves as part of the piercing apparatus 
as well as part of the channel through which blood is drawn. (Examples: 
mosquito, Fig. 97; tabanus, Fig. 156.) From the floor of the mouth cavity, at 
the base of the labium, there arises a fleshy organ, the hypopharynx or lingua. 
The hypopharynx bears the opening of the common salivary duct and in many 
insects becomes an important part of the mouth. 

The mandibulate type of mouth parts is regarded as the primitive arrange- 
ment of the head appendages entering into the formation of the organs for 
obtaining food. These appendages have become highly modified in many 
insects and, in some cases, as in the lice and muscoid flies, are so changed 
that the parts have not been definitely homologized with those of the primitive 
type. The various types of mouth parts found in bloodsucking insects are 
discussed more in detail under the different groups but one or two simple 
bloodsucking types may be compared with the mouth parts of the grasshopper. 

Mouth Parts of the Bedbug (Cirnex lectularius) : In the bedbug the mouth 
parts are rather highly specialized. The labium (Fig. 46 La) has become 
greatly elongated and divided into three well-defined segments. Along its 
dorsal surface there is a groove or gutter within which lie the piercing organs, 
the mandibles and maxillae. The segments of the labium are flexible and can 
be telescoped on each other by internal muscles. Each mandible is a delicate, 
chitinous, needlelike rod, which arises deep in the head and terminates in a 
sharp point, the distal part being supplied with fine recurved teeth (Fig. 46 M) . 
The maxillae (Mx), arise close beside the mandibles but are stouter and slightly 
longer. They are grooved on the inner face and, just in front of the hypo- 
pharynx, form, by apposition, two canals (Fig. 46). They are interlocked 
throughout their entire length and firmly adhere even when dissected out of 
the head. In cross section the two canals are distinctly shown, the larger one 
serving as the food channel up which the blood is drawn by the pharyngeal 
pump; the smaller one is the channel down which the secretions of the salivary 
glands are forced into the wound by the salivary pump. The labrum or 
labrum-epipharynx is a large structure lying over the base of the labium. On 
the under surface, lying at the base of the labium, is the fine-pointed hypo- 
pharynx (Fig. 46 Hyp) through which is discharged the salivary secretion 
into the groove formed by the maxillae. The salivary pump is a complicated 



THE HEXAPODA: INSECTS 



13* 




Fig, 45. Mouth parts of a grasshopper. {A) Frontal view of the labrum attached to the 
clypeus. (B) Looking into the mouth of a grasshopper with the mandibles removed and 
the labrum turned back. (C) The lower side of a mandible with the tendons in place. 
(D) The upper side of a mandible. (E) and (F) The right and left maxillae as viewed 
from the lower or ventral side. (G) The labium as viewed from the lower side. C, cardo; 
Cd, socket for condyle of mandible; Clp, clypeus; Cx, condyles of mandibles; Ephy, epj- 
pharynx; Fc, area over which fits the base of the mandible; Ga, galea; Gl, glossa; Hphy,. 
hyopharynx; IN, cutting teeth of mandible; Lb, labium; LbPlp, labial palpi; Lc, lacinia; 
Lm, labrum; M, opening into mouth; Mb, molar portion of mandible; Met, mentum; 
MX, upper or dorsal surface of maxilla; MxPlp, maxillary palpi; Pgl, paraglossae; Plf, 
palpigerj-Sga, subgalca; Sm, submentum; St, stipes, Ten, tendons; Tr, torma. 



MEDICAL ENTOMOLOGY 




F/^. 46. The mouth parts of the bedbug (Cimex lectularius}. (a) Frontal view of the 
mouth parts and part of the head. () Ventral view of the pharynx and salivary gland con- 
nections with the hypopharynx. (c) The salivary pump partially opened, (d) Cross section 
of the maxillae and mandibles. Ant, antenna; C, extension of body cavity into maxilla; 
Cl, clypeus; E, eye; Fc, food channel; Hyp, hypopharynx; La, labium; Lb, labrum; LG, 
labial gutter; M, tip of mandible, greatly enlarged; Md, mandible; Ms, muscles that move 
the piston; MX, maxilla; P, piston head; Ph, pharynx; PR, piston rod; O, esophagus; 
SC, salivary channel; Sd, salivary duct; SG, common duct of salivary glands; Sp, salivary 
pump. 

organ, but its structure and function have been elucidated by Patton and 
Cragg (1913) and Puri (1924). It is located on the ventral surface of the 
hypopharynx; it is cup-shaped in general appearance and about one-tenth the 
size of the pharyngeal pump. Its posterior end is closed by an elastic membrane, 
a part of which is invaginated to form a chitinized piston (Fig. 46). Posteriorly 



THE HEXAPODA: INSECTS 133 

the piston is continued as a flattened rod to which retractor muscles are 
attached on each side. The salivary duct opens into the pump on the ventral 
side by a crescent-shaped opening. The working of the pump is brought 
about by the movement of the piston. When the piston is withdrawn, salivary 
secretion is drawn into this chamber. The relaxation of the retractor muscles 
is followed by the recoil of the elastic posterior membrane of the pump, which 
forces the piston into the chamber and the saliva is sent down the duct in the 
maxillae into the wound. The recoil of the piston closes, at the same time, 
the opening of the salivary duct leading from the glands. The saliva in blood- 
sucking insects seems to perform certain definite functions, either to prevent 
coagulation or to induce blood flow to the invading mouth parts, jj 
| Another important organ in connection with the bloodsucking type of 
mouth parts is the pumping pharynx or pharyngeal pump, an organ whose 
special function is to pump the blood from the host and pass it on to the 
intestine. In the bedbug the organ is well developed. It is pear-shaped in out- 
line, but flattened dorsoventrally. In sectional view the lumen appears as a 
transverse slit. The pumping action is brought about by powerful dilator 
muscles attached to the dorsal surface; these dilate the pharyngeal cavity, and 
blood flows in through the food channel (Fig. 46). The relaxation of the 
muscles allows the resilient chitinous walls to come together and thus probably 
forces the blood on through the esophagus. | 

Mouth Parts of Other Bloodsucking Insects: In other bloodsucking insects 
various modifications occur. In the mosquito (Fig. 97), it is the labrum- 
epipharynx that forms the food channel. These organs, together with the 
mandibles and maxillae, constitute the piercing apparatus. The salivary secre- 
tion is pumped into the wound through a channel in the hypopharynx. The 
pharyngeal pump is well developed and functions as in the bedbug, though 
here the pharynx must connect with a different food channel. The structures 
employed by various insects in piercing a host and withdrawing blood are 
in need of more detailed study, and some of these problems will be stressed 
under the discussion of the various bloodsucking groups. 

Mouth Parts of Some Muscoidean Plies: Another type of mouth parts of 
great interest to the medical entomologist is that found in many of the 
muscoidean flies as, for example, the housefly, the flesh flies, the bluebottle 
flies, and others. Here the food is taken in one of three ways: (i) the flies 
may obtain their food in liquid form as nectar, milk, sugar solutions, the 
liquid exudates of decaying substances (as pus, fecal matter, sewage, etc.), 
perspiration, serum exudates from wounds, moisture from around the eyes, 



i 3 4 MEDICAL ENTOMOLOGY 

or other sources; (2) or they may liquefy soluble substances such as sugar by 
regurgitating liquid from their intestines or by using the salivary secretion 
and then suck up such fluids by their mouth parts; (3) or they can ingest 
larger particles by applying the mouth opening directly to soft substances. This 
type is very complicated and may be best illustrated by the mouth parts of 
the housefly. 

In the housefly the mouth parts constitute an elongated proboscis, which, 
when not in use, is partly withdrawn into the head capsule. When the fly is 
about to feed, the proboscis is extended by compression of the body, thereby 
forcing blood into the open spaces of the proboscis, and the tracheae and air 
sacs become distended with air (Fig. 47). The proboscis then hangs downward 
from the head capsule. This distension may be produced artificially by soaking 
the head in 10 per cent caustic potash, then placing it under a dissecting 
microscope, and pressing on it with a needle; the proboscis and labella may 
be extended and partially contracted at will. The proboscis may be divided 
into three distinct regions the rostrum, the haustellum, and the oral disc 
( Fi g- 47)- 

THE ROSTRUM (Fig. 47 R) : In side view the rostrum appears like a truncated 
pyramid, the base attached to the head capsule. Its wall (W) consists of a rather 
tough chitinous membrane that is attached to the ventral margin of the head 
and is continuous with that of the haustellum and the oral disc. Within the 
membrane is the large pharyngeal sclerite or fulcrum (Fig. 47 Fa), and 
within the fulcrum lies the pumping pharynx and its dilator muscles. In side 
view the fulcrum appears like a Spanish stirrup iron, while the frontal aspect 
presents an inverted vaselike appearance. The sides of the fulcrum are roughly 
triangular in outline and are produced at their proximal ends into a pair of 
stout cornua. The anterior angles are joined by the clypeus (tormae of Peter- 
son) and the anterior arch (Fig. 47). Posteriorly they are joined by a thinner 
convex plate, the posterior plate, which forms the rear wall of the pharynx. 
The anterior wall of the pharynx consists of a thin chitinous plate, thickened 
along its median line to form a sharply delimited chitinous rod, the median 
ridge. To this ridge are attached the dilator muscles of the pharynx. Its distal 
end terminates opposite, and in close contact with the prepharynx (hyoid 
sclerite) ^The pharynx unites at its proximal end with the esophagus, and its 
distal end joins the tube formed by the mouth parts by way of the hyoid 
sclerite, which surrounds the buccal opening. By means of the retractor mus- 
cles the anterior wall of the pharynx is withdrawn from the posterior wall, 
and by this action liquid food is sucked up through the mouth parts and 
passed into the esophagus. Below the fulcrum, on either side of the middle line, 



THE HEX APOD A: INSECTS 



135 



there are two slightly chitinized plates. From each of these arises a single- 
jointed, somewhat club-shaped maxillary palpus) Near the border of the max- 
illary plates there arises on each side of the fulcrum a sinuous, strongly 
sclerotized rod; the apices of these rods articulate in small pits at the sides of the 
broad base of the labrum-cpipharynx and function in the extension and retrac- 
tion of the proboscis( Below the palpi the rostrum narrows and merges with 
the haustellum.'j 



MO 




Fig. 47. A somewhat lateral view of the proboscis of the housefly (Mnsca domestica). 
R, rostrum; H, haustellum, OD, oral disc; MO, mouth opening; Cxc, a main collecting 
channel of the psaulotracheac; DSc, cliscal sclerite; Fc, fcxxl channel bAtffcen the hypo- 
pharynx (Hp) and the labrum (Lm); Fu, fulcrum seen in outline beneath the chitinous 
membrane (W); Hp, hypopharyiix; LA, label la; Lg, labial gutter; Lm, labrum; MR, 
maxillary rods (stipes); MxPlp, maxillary palpi; Ptr, pseudotracheae; Th, theca; W, 
membrane of proboscis. 

THE HAusTELLt'M (Figs. 47,48) : The haustellum (H) is attached to the distal 
end of the rostrum and gradually narrows to its junction with the oral disc. 
In the housefly, as in many of the higher Diptera, all the mouth parts are 
not present. The mandibles and maxillae are lacking though the palpi of the 
maxillae still persist. The mouth parts consist of the labrum-epipharynx, 
the liypopharynx, and the labium. The rear portion of the haustellum is the 
lubium. Its structure is complicated and not well understood. The posterior sur- 
face consists of a large, concave sclerite, the mentum or theca, which is 
articulated with the base of the haustellum; its apex rests on peculiar rods 
that articulate with the oral disc. The anterior face of the labium is deeply 
grooved (labial groove), and the margins of the groove are supported by 



136 MEDICAL ENTOMOLOGY 

stout rods (Fig. 48 LR) that extend from the base to articulate with the 
discal sclerite. The mentum and the anterior groove are connected on each 
side by tough membranes, Lying in the labial groove or gutter are the labrum- 
epipharynx and the hypopharynx. The labrum-epipharynx (Lm) is in front. 
It consists of an elongate, pointed organ that is deeply channeled on its posterior 
face (Fig. 48). The hypopharynx lies directly behind the labrum-epipharynx; 
it is an elongate bladelike structure (Hp) with a groove in its anterior face. 
The margins of these two fit closely into each other and thus form the food 
channel (Fc). The tips of the labrum-epipharynx and hypopharynx extend 
to the opening formed by the discal sclerite; their bases are united and lead 
to the mouth opening, which lies between thern. ) 

CTIIE ORAL DISC (Figs. 47,48) : The oral disc (OD) consists of the discal sclerite 
(DSc) and the labella, the two large lobes that arise from the discal sclerite. 
The labella are shown fully expanded in the figures. When not in use they are 
greatly reduced in size. The oral disc articulates to the distal part of the haustel- 
lum by means of two joints. The anterior joint is formed by the junction of 
the labellar rods to the discal sclerite by means of tendons. The discal sclerite 
is somewhat horseshoe-shaped, the opening being anterior; posteriorly there 
extends a stout thickening of the sclerite. This sclerite surrounds the mouth 
or oral opening, and to it are attached the pseudotracheal membrane and 
the prestomal teetK^The posterior joint of the oral disc is formed by a pair of 
rods (the sigma or metofurcal bars) that rest on two arms of the triradiate 
labellar sclerite or furca. These rods arise from the forks of the mentum 
(Fig. 4 8Th). 

The two labellar lobes are completely separated from each other by a deep 
fissure, which is continuous anteriorly with the labial groove or gutter; the 
fissure extends some distance on the posterior face. Each labellum contains a 
large hemocele and is filled with blood when extended. In the resting condi- 
tion the two inner walls of the labella are in close contact, but when feeding 
they are widely separated. As the walls are very soft they can be molded to 
any surface on* which the fly is feeding. The inner surface of each labellum 
is traversed by a series of channels that resemble tracheae, hence are called 
"pseudotracheae" (Figs. 47,48 Ptr). Through these pseudotracheae the fly 
sucks up its liquid food. As the size of the opening to these channels deter- 
mines what materials the fly can ingest, the structure of these organs is of the 
utmost importance. The inner wall of each labellum consists of a very thin, 
structureless membrane in which lie the pseudotracheal channels. These chan- 
nels all converge to the prostomum or opening bounded by the discal sclerite. 
In each labellum are 30 to 32 of these grooves; the upper 9 or 10 and the lower 



THE HEXAPODA: INSECTS 137 

15 or 16 unite to form collecting channels (Figs. 47,48 Cxc), and the middle 
5 or 6 open directly into the prostomum. Each pseudotracheal channel is kept 
open by means of incomplete rings of chitin. Each chitinous ring is bifid at 
one end and simply expanded at the other. The rings are closely set and 
alternate so that a bifid end faces an expanded end, and then an expanded end 
faces a bifid end. Looking along the surface of a channel there appears a 
series of alternate bifid and expanded ends of chitinous rings (Fig. 48 d,e,j) . 
The membrane of the labellum is stretched taut over all these rings except 
between the bifid ends and the line between the expanded ends and the forks. 
Therefore, the only openings into the channel itself are between the forks 
of the bifid end of each ring and a zigzag fissure extending the whole length 
of the channel. The openings between the bifid ends have been called the 
"interbifid grooves." During feeding the membrane is stretched so taut that 
the zigzag fissure is practically closed and the only food that can enter is 
through the interbifid grooves. The size l of the interbifid grooves determines 
the size of the solid particles that can pass into the food channel. This position 
of feeding has been termed by Graham-Smith "the filtering position." .,) 

By separating the labella further there is brought into play the prestomal 
teeth (Fig. 49). These teeth arise from the lateral margin of the discal sclerite, 
five on each side. Each tooth consists of a chitinous strip, serrate on its distal 
extremity, and lies between the openings of two pseudotracheae. Graham- 
Smith (1930) has shown that instead of one row of prestomal teeth there 
are four rows in the blowfly (Calliphora erythrocephala). This also appears 
to be the condition in the housefly. The first three chitinous strips that sur- 
round the pseudotracheal openings into the oral cavity are not bifid but 
sharply pointed (Fig. 49 O). These may correspond to the extra teeth described 
for the blowfly. Following these are the ordinary chitinous rings that keep 
the pseudotracheae open. 

(^Recently Graham-Smith has described three methods of feeding by the 
blowfly; the housefly, in all probability, feeds in the same fashion.(The first 
method, the filtering method, has already been described. By further separat- 

1 Graham-Smith has measured these interbifid spaces and the channels in several 
of our common flies. These are here appended. 

Pseudotracheae, Interbifid spaces, 

diameter (mm.) diameter (mm.) 

Proximal Distal Proximal Distal 

end end end end 

Calliphora erythrocephala 0.02 o.oi 0.006 0.004 

Sarcophaga carnaria 0.02 o.oi 0.005 0.004 

Lucilia caesar 0.02 o.oi 0.006 0.004 

Fannia canicularis o.oi 6 0.008 0.006 0.004 

Musca domestica 0.016 0.008 0.004 0.003 




Fig. 48. Detailed illustrations of the mouth parts of the housefly (Musca domestica). 
(a) Lateral view of the proboscis of the housefly. () Frontal view of the proboscis with 
the labella expanded, (c) Cross section (somewhat diagrammatic) of the middle of the 
haustellum. (d) View of a pseudotracheal channel (highly magnified) as seen through 
the integument of the labellum; the right half illustrates the details of a channel with 
the ch Hi nous rings in place; the upper left side shows two interbifid grooves in the in- 
tegument with the chitinous rings showing through; the lower left corner shows a single 
interbifid groove which leads to an interbifid space, (e) A single chitinous ring in side 
view showing the attachment of the interbifid groove to the forks of the ring. (/) Two 
chitinous rings as they are arranged in a pseudotracheal channel (partial side view). 
H, haustellum; OD, oral disc; R, rostrum; A, anterior arch of fulcrum; Ap, anterior wall 
of pharynx; Cl, clypeus; Cxc, main collecting channels; DSc, discal sclerite; F, fissure 
along the surface of the pseudotrachea; Fc, food channel; Fu, fulcrum; Hp, hypopharynx; 
IG, interbifid groove; IS, interbifid space, LA, labellum; Lm, labrum; LR, labellar rods; 



THE HEXAPODA: INSECTS 



139 



ing the labella the prestomal teeth can be brought into action and used for 
scraping the scraping position. By an extreme folding back of the labella 
the mouth or oral opening can be brought into direct contact with the food, 
and then comparatively large objects can be ingested, as the eggs of helminths. 
By various manipulations of these methods the fly can feed on a great variety 
of substances. Furthermore, liquid can be regurgitated (the vomit drop) to 
dissolve what has been scraped loose (Fig. 50). Graham-Smith also states 
that the prestomal teeth, moistened with infected vomit, appear to be excellent 




Fig. 49. Looking into the mouth opening of the housefly (only a small part 
is shown). ACCH, anterior collecting channel; DS, discal sclerite; MO, mouth 
opening; O, openings to the pseudotracheal channels, PCCH, posterior collect- 
ing channel; PT, prestomal teeth. 

instruments for the intradermal introduction of pathogenic organisms. Sites 
on the body most likely to be selected for scraping are mucus and conjunctival 
surfaces, recent abrasions, and wounds, ; 

The mouth parts of other insects that afTect man are briefly discussed under 
the different species described in the following pages. 

LSc, labellar sclerite; M, membranous portion of the pseudotracheal channel; MO, open- 
ing to the food channel; MR, maxillary rods (stipes); Mt, mentum; MxPlp, maxillary 
palpus; O, esophagus; Ph, pharynx; Pph, hyoid or prepharyngeal sclerite; Pr, pseudo- 
tracheal ring of ehitin (the dotted portion indicates the position of the ring at the rear of 
the channel); Ptr, pseudotracheae; Sc, salivary channel in hypopharynx; SD, salivary 
duct; Sp, salivary pump or syringe; Th, theca or mentum; W, membranous wall of 
proboscis. 



i 4 o MEDICAL ENTOMOLOGY 

THE ANTENNAE: The antennae are the modified appendages of the 
second head segment. Each antenna arises from a small antennal sclerite situ- 
ated in the antennal fossa. The antennae show various modifications in the 
different orders and names have been applied to them such as setaceous, fili- 
form, clavate, and capitate. Some of the types found in insects of medical im- 
portance are shown in Fig. 51. The number of antennal segments varies 
widely. The first segment is known as the scape and the second as the pedicel; 




Fig. 50. The housefly, Musca domestica, showing the .vomit spot at the tip of labella. 
(Modified from Hewitt.) 

the remaining segments constitute the flagellum (Fig. 51). The various func- 
tions of the antennae are not well known. It has been fully established that 
the sense organs of touch and smell are present on the antennae and possibly 
also some of the organs of taste. 

THE THORAX 

The thorax is the second region of the body. It is attached to the head by 
an intersegmental region known as the neck. The neck is not sclerotized 
except for a few small sclerites, the cervical sclerites. The thorax consists of 
three segments and bears the wings and legs. The segments are known as the 
prothorax, mcsothorax, and metathorax (Fig. 52) . The terms pro, meso, and 
meta are used to designate the first, second, and third segments of the thorax 
and also the various part| of these segments. For example, the protergum, 
proepisternum, etc., refer to the tergum and episternum of the prothorax. The 



THE HEXAPODA: INSECTS 141 

pleuron of each thoracic segment is usually divided into two sclerites the 
anterior one being called the episternum (Fig. 52 Eps) and the posterior 
the epimeron (Epm) and these bear the prefixes, pro, meso, or meta to indicate 
to which segment they belong. Each segment, in its simplest form, consists of 




Fig. 51. Various types of insect antennae. (/) Musca domestica. (2) Wohljahrtia vigil. 
(3) Aedes acgypti. (4) Glossina paJpalis. (5) Tabanus flauiis. (6) Cimcx lectularis. (7) 
Xenopsylla cheopis. (Not drawn to the same scale.) A, arista; ds, dorsal suture or seam; 
Fl, flagellum; p, pedicel; s, scape. 

a dorsal region, the tergum or notum; a ventral region, the sternum; and two 
sides, the pleura (singular pleuron) or pleurites. Each of these regions may 
consist of one or several sclerites separated by sutures. A rather simple type 
of thorax is that of the grasshopper (Fig. 52) . It is more or less cylindrical in 
shape. Here the tergum (PN) of the prothorax is greatly enlarged; it overlies 
a large part of the mesothorax and extends down on the sides to near the 



I 4 2 MEDICAL ENTOMOLOGY 

attachment of the first pair of legs. Only a small portion of the lateral wall is 
visible the episternum (Eps t ) of the prothorax; the epimeron is entirely 
concealed and lies underneath the lower end of the tergum. 

The mesothorax is shown in dotted lines beneath the pronotum. The epi- 
sternum (Epso) and the epimeron (Epm 2 ) are well developed, and from 



Epi, 




b 



Fig. 52. The external structure of the thorax of a grasshopper (Mclanoplns difterenti- 
alis). (a) Prothorax with the leg attached. () Lateral view of the incso- and metathorax 
(pterothorax) with the first segment of the abdomen; the prothorax sketched in outline. 
(c) Ventral view of the entire thorax. Cx, coxa; Epnis, Epnn, epimera of nieso- and 
metathorax; Epsi, Epsi, Epss, episterna of pro-, mcso-, and rnetathorax; F, femur; iS, 
sternum of first abdominal segment; iiSp, iiiSp, spiracles of second and third thoracic 
segments; L, lateral lobes of the metasterna; PN, pronotum; S, a suture; Si, Sj, S.t, pro-, 
meso-, and metasterna; Sa, invaginations of sternal apodcmes (furcae); iSp, first spiracle 
of abdomen; T, tympanum; Ta, tergum of mesothorax; Tar, tarsus; Tb, tibia; Te, tergum 
of first abdominal segment; Tg, tergum of metathorax; Tr, trochanter; W, cut end of 
wings; WP, wing processes. " 

their lower ends arises the second pair of legs. The metathorax is also large 
and the pleurites (Eps ;{ and Epm ;{ ) are well outlined. Their tergal portions 
underlie the pronotum and the wing bases. It is well to note that the meso- 
and metathorax of the grasshopper are each much larger than the prothorax, 
owing to the presence of wings. This enlargement is to provide for the 
processes for wing attachment and the large muscles needed to move these 




THE HEX APOD A: INSECTS 143 

organs of flight. In the Diptera, where only the mesothoracic wings are 
present, the mesothorax (Fig. 53) is greatly enlarged and appears to occupy 
the entire thoracic region. 2 In the Culicidae the thorax is distinctly wedge- 
shaped, the thick part of the wedge occupying the dorsal surface. The pro- 
thorax is greatly reduced. The pronotum is represented by two sclerotized 
areas on each side (Fig. 53 PN,PPN) the anterior pair being joined by a narrow 
membrane lying in front and 

J WTO 

somewhat beneath the mesono- 
tum. The posterior pronotum has 
generally been called the proep- 
imeron and probably corre- 
sponds to the humeral callus of 
the higher Diptera. The pleuron 
consists of a small episternum as 
in the grasshopper. The meso- 
thorax occupies the greater part 
of the thorax. The mesonotum 
(Mcs) extends from the head to 
the scutcllum (Sc) and appears to 
occupy the entire dorsal surface. 
The scutellum (Sc) belongs to 
the mesothorax and is separated 
from the mesonotum by a distinct 
suture. Viewed from the dorsal 
surface it is trilobed and each lobe 
bears a distinct group of bristles. 
Directly behind and below the 
scutellum is a large, smooth, chitinized area, the postnotum (P). The side of 
the thorax is largely made up of the mesopleuron. It begins directly in front of 
the mesothoracic spiracle (iiSp) and extends to the suture cephalad of the 
metathoracic spiracle (iiiSp). Unlike that of the grasshopper, the episternum in 
the flies is divided into two distinct parts, the so-called mesanepisternum and 
the meskatepisternum. The latter sclerite is generally called the sternopleuron 
in all the Diptera. The mescpimeron is a large, rectangular-shaped sclerite. Be- 
hind it lies the metathorax, greatly reduced in size and united rather firmly to 
the abdomen. The metanotum (N) appears as a very narrow band lying be- 
hind the postnotum and articulating with the tergum of the first abdominal 

2 The thorax of the various orders of insects treated in this work is discussed under 
the groups in later chapters. 



Fig. 55. Lateral view of the thorax of a mos- 
quito (Psorophora sp.). C, cervical slccrite; Cx, 
coxa; EpiTb, Epms, cpimcra of the meso- and 
metathorax; Epsi, Epsz, Epsa, episterna of the 
pro-, meso-, and metathorax; H, haltere; iiSp, 
iiiSp, spiracles of meso- and metathorax; M, 
meron; Mes, mesonotum; N, notum of meta- 
thorax; P, postnotum of mesothorax; PN, prono- 
tum; PPN, postpronotum; Sc, scutellum; Stn, 
sternum; WP, cut ends of wing. 



I44 MEDICAL ENTOMOLOGY 

segment. Laterally the metathoracic spiracle is found in the me.tepisternum, 
and directly behind this sclerite is the metepimeron, rather faintly delimited 
from it. Directly above the latter sclerite is found the haltere (H). Located 
above and between the coxae of the second and third pair of legs is the so- 
called meron (M). 

In the mosquitoes, as in nearly all the Diptera, the pleural sclerites bear 
groups of hairs or spines that are of great taxonomic significance. For an 
account of the pilotaxy, see pages 256-258. 

The Appendages of the Thorax 

THE LEGS (Fig. 54) : Each segment of the thorax bears a pair of legs. Each 
leg is articulated to the thorax by its basal segment, the coxa, located in the 
membranous area between the pleural plates the episternum and epimeron 
and the adjacent parts of the sternum. An insect's leg consists of five distinct 
parts : 

The coxa (Cx) varies greatly in size and shape in different insects. It may 
be firmly attached to the body wall or very movable, as in the housefly and 
grasshopper. 

The trochanter (Tr) is a small segment of varying shape and forms the 
attachment point for the next segment, the femur. <+ 

The femur (F) is usually an elongated segment and may be greatly en- 
larged as in jumping and leaping insects; e.g., grasshoppers and fleas. 

The tibia (Tb) is usually slender, nearly always as long or longer than the 
femur, and frequently bears many stout hairs or spines. The tip may be 
armed with special spines. 

The tarsus (Tar) is generally divided into segments, five being the most 
common number. There may, however, be only one segment as in the lice, two 
in plant lice, three in some grasshoppers, etc. The first segment is frequently 
greatly elongated and has been called the metatarsus. Some of the segments 
may be heavily armed with spines or stout setae. The last segment is generally 
provided with a pair of claws (Fig. 54 C). The claws arise from a special 
elongation of the last joint. The claws are frequently modified and adapted 
for various purposes and are moved by rather powerful retractor muscles. 
In some groups, as the lice, and some Mallophaga, there is only a single 
claw, which is adapted for clinging to hairs. The claws may be simple, 
toothed, equal in size, or one claw may be much larger than the other. 

On the ventral surface of the claws and attached to the membrane of the 
last tarsal segment is a pair of membranous pads, the pulvilli (Fig. 54 P). Each 
pulvillus may be provided on its ventral surface with numerous, glandular 



THE HEXAPODA: INSECTS 145 

hairs, the so-called tenent hairs. It is by means of these tenent hairs (each 
one is connected with a gland) that flies are enabled to walk on ceilings, glass, 
and other smooth surfaces. The sticky excretion gathers up all sorts of bac- 
teria, spores, cysts, and filth and distributes them. Between the pulvilli and 
below them is a long, narrow, hairy spine, the empodium (E). The empodium 
varies greatly in different insects. It may be hairlike, it may be a stout spine, 
or it may be padlike and then it is said to be pulvilliform. 




Fig. 54. The legs of insects, (a) Hind leg of a grasshopper, (b) Tarsus and pretarsus of 
leg of grasshopper, (c) Leg of housefly (Musca domestica). (d) Pretarsus of housefly, (e) 
Tip of tarsus and pretarsus of fly (Stratiomys). A, arolium; C, claw; Cx, coxa; E, empo- 
dium; F, femur; P, pulvillus; PI, unguitractor plate; Ptr, pretarsus; T, tendon of muscle 
attached to unguitractor plate; Tb, tibia; Tar, tarsus; Tr, trochanter. 

THE WINGS: Probably the most important appendages of the thorax' 
are the wings. They are not true appendages but are outgrowths from the 
dorsolateral margins of the meso- and metathorax. 

In insects with incomplete metamorphosis, as the Orthoptera and Hemip- 
tera, the external development of the wings may be easily observed. In holo- 
metabolous insects, as the Diptera, Lepidoptera, and other orders, the wings 
are developed internally during the larval growth and only become exposed as 



146 



MEDICAL ENTOMOLOGY 



the wing pads at the time of pupation. 3 The great majority of insects possess 
two pairs of wings, though the Diptera have only one pair, the metathoracic 
wings being represented by the halteres or balancers, vestiges of what may 
have been originally wings (Fig 53 H). Some orders are wingless, as the 
Anoplura (lice) and Siphonaptera (fleas), though they undoubtedly de- 
scended from winged ancestors. The Apterygota consists of two or three 
orders in which the wingless condition is primitive. 

The wing as seen in an adult insect consists of two fused membranes. The 
longitudinal thickenings, the veins (Fig. 55), are more heavily chitinized 
areas laid down around the cavities through which tracheae supplied the 
developing wings with air. The complete system of veins in a wing is called 




Fig. 55. Hypothetical tracheation of a wing of a primitive nymph. (After Comstock.) 

its venation or neuration. The venation presents excellent characters in sys- 
tematic work, and various systems of naming these veins have developed in 
each order. Comstock and later Comstock and Needham developed what 
they called the hypothetical type of venation (Fig. 55) of a primitive winged 
insect. As all winged insects are believed to have descended from a common 
ancestor, many extensive studies have been carried on to interpret the vena- 
tion of the wings in the various orders. As a result of Comstock and Need- 
ham's work, a uniform system of naming the veins was evolved, though un- 
fortunately it has not been adopted by all taxonomic workers. In fact, there 
are many systems and each author follows his own bent in naming the veins. 
In medical entomology it is necessary to have a thorough knowledge of the 
venation in the Diptera, and the discussion here is largely restricted to that 
order. 



3 For a full account of the development of wings and wing venation, consult Comstock 
(1918, 1947) or Imms (1934). 



THE HEXAPODA: INSECTS 147 

The principal veins in an insect's wing consist of a series of longitudinal 
veins and a few definite cross veins. Modification of the hypothetical type 
takes place through addition or reduction, mainly, reduction in the dipterous 
wing. Reduction occurs through fusion of veins or their loss. These modifica- 
tions are differently interpreted by various workers so that uniformity cannot 
be looked for in taxonomic work. The arrangement of the veins and cross 
veins in the hypothetical type is shown in Fig. 55. The following table gives 
the nomenclature of the veins according to the Comstock-Needham system 
and to the system used extensively by the students of the Diptera. 

Terminology Comstoc\- Abbreviations 

of Need ham 

dipterists terminology 

Costal Costa C 

Auxiliary vein Subcosta Sc 

ist longitudinal vein Radius one R, 

2nd longitudinal vein Radius two and three R 2 and R 3 

3rd longitudinal vein Radius four and five R 4 and R 5 

4th longitudinal vein Media one M, and M 2 

Media two 

5th longitudinal vein Media, 3rd, and M :i and Cu, or Cu 

Cubitus, or Cubitus 
alone 
6th longitudinal vein Anal veins lA, 2A, 3A 

Figs. 56 and 57 present die wing of a Tubanus species with the veins and 
cells labeled according to the Comstock-Needham system and that com- 
monly used by dipterists. 

The costa (C) is the thickened frontal margin of the wing; the anterior 
border is generally called the costal border. 

The subcosta (Sc) is directly behind the costa and parallel to it; it is generally 
known as the auxiliary vein (Fig. 57 a) by dipterists. In the Diptera the sub- 
costa is rarely branched. 

The radius lies directly behind the subcosta and, in the hypothetical type, 
is five-branched. In Tabanus the radius is four-branched, R ;{ having been lost 
by fusion with Ro. The first branch, R,, is simple and corresponds to the first 
longitudinal (Fig. 57 ist). Near the base of the wing a short branch, the 
radial sector (Fig. 56 Rs), arises, which divides into two branches, the posterior 
branch again dividing. The first branch constitutes the 2nd longitudinal vein 
(Fig. 57 2nd) ; the posterior branch with its two divisions is the 3rd longitudinal 



i 4 8 



MEDICAL ENTOMOLOGY 



The media extends through the middle of the wing. In Tabanus it is three- 
branched (Fig. 56 Mj, M 2 , M 3 ). The first two branches constitute the 4th 
longitudinal vein (Fig. 57 4th). 

The cubitus is typically two-branched and with the posterior branch of 
media (M 3 ) constitutes the 5th longitudinal vein (Fig, 57 5th). 




Fig. 56. Wing of Tabanus sp. with the veins and cells labeled according to 
the Comstock-Needham system. 



costal 



2nd 




3rd 



6th 



5th 



Fig. 57. Wing of Tabanus sp. with the veins and cells labeled in accordance 
with the system followed by students of the Diptera (flies). 

The anal veins are the two or three veins (ist, 2nd, and 3rd when present) 
lying behind the cubitus. In the Diptera the first anal vein is greatly reduced 
or absent. It is frequently represented by a furrow, the anal furrow, which is 
close behind the cubitus. The second anal vein is well preserved (Fig. 56 2d A) 
and corresponds to the 6th longitudinal (Fig. 57 6th). 

The cross-veins include several well-marked veins. These are (i) the 
humeral (h), (2) the radio-medial (r-m), known also as the anterior cross- 
vein (ac), and (3) the medio-cubital (m-cu), commonly called the posterior 



THE HEXAPODA: INSECTS 149 

cross-vein (discal cross-vein of Williston; Fig, 57 pc). The radio-medial or 
anterior cross-vein is very constant, and its location will always give a clue 
to the venation of the wing. Another important cross-vein is the medial (m). 
The areas of the wings bounded by veins are called ceils. In the Comstock- 
Needham nomenclature the cell takes the name of the vein lying immediately 
in front of it (Fig. 56) . In the older system the names of the cells are rather 
arbitrary, and it is at times difficult to interpret an author's work unless he is 
very specific in his explanations (Fig. 57). 

THE ABDOMEN 

The abdomen constitutes the third region of the body (Fig. 58). It is 
composed of a series of segments that retain the rather primitive annular form. 



DV 




viS 



viiS 



viiiS 



viiiSp 



Fig. 5<S. Lateral view of the abdomen of a grasshopper (Melanoplus differentialif'). 
Cer, cercus; Cxc, coxal cavity; E, egg guide; Ep, epiproct; Epma, epimeron of 3rd thoracic 
segment; Lc, lateral commisure; Ovi, ovipositor consisting of the dorsal valves (DV), 
ventral valves (VV), and inner valves (IV); Pp, paraproct or podical plate; Ss sternum of 
third thoracic segment; iS-viiiS, first to eighth abdominal sterna; iSp-viiiSp, one to eight 
spiracles; iT-xiT, one to eleven tergites or terga; T, tympanum. 

Each segment has a large tergum and a well-developed sternum. The pleural 
region is nearly always membranous, though differentiated sclerites may 
sometimes occur. When the abdomen of a grasshopper is examined, it will 
be observed that the terga and sterna closely approach each other while the 
pleurum is represented by a folded membrane, the longitudinal conjunctiva. 
The abdomen consists of eleven segments, the last three or four being modi- 
fied to form, with the modified appendages, the clasping organs of the male or 
the ovipositor of the female (genitalia). Though eleven segments are con- 
sidered the primitive number, it is often difficult to recognize more than eight 




150 MEDICAL ENTOMOLOGY 

or even less. This is due to their reduction or modification in the higher 

orders such as the Diptera and Hymenoptcra. 
The terminal segments with their appendages are highly modified in many 

insects to form, in the males, the most bizarre types of clasping organs. As 

the parts entering into the external genitalic structures have not been homolo- 

gized throughout the various orders, it 
does not seem worth while to discuss 
them as they occur in the more gen- 
eralized groups. These structures will be 
dealt with in some detail in those groups 
that are of importance from the stand- 
point of medical entomology. 

INTERNAL ANATOMY 



The internal anatomy of insects can be 
referred to only briefly. Those structures 
that chiefly interest the medical entomolo- 
gist will be outlined in brief detail, i.e., the 
F/e. 50. Diagrammatic cross section j. t . , i 

t L i i i r L LJ c digestive system and its appendages, the 

of the third segment or the abdomen of ' rr ' 

a grasshopper to show position of mus- respiratory system, the blood, the muscu- 

cles and some of the internal organs, lar system, and the reproductive system. 

Em, external lateral muscles; F, fat 

body; Fc, food channel or alimentary T cvQTPlv/f 

canal; H, heart; L,, internal lateral mus- THE DIGESTIVE SYSTEM 

clc; la, lateral apodemes of sternum; AND ITS APPENDAGES 

Lm, lateral internal dorsal muscle; Mi, 

median internal dorsal muscles; mp, The most striking feature of an insect 

Malpighian tubules; P, an external mus- is that the body wall (p ig ^ orms the 

cle; ps, perivisceral sinus for blood; R. , , . . . 

reproductive organs; &, &, dorsal and skeleton, giving support and protection to 

ventral sinuses; Ta, ventral diaphragm; the internal organs. The body wall may 

Tn, dorsal diaphragm; Tr, trachea; V, represent the wall of a cylinder. The ali- 

ventral I muscles; V X) ventral nerve cord. j . , 

(Modified from Snodgrass.) ... 

central position in the cylinder and con- 
nects the mouth opening with that of the anus. It may be barely as long as the 
body or it may be coiled and doubled on itself, making several convolutions. 
Above it lies the heart, and the nerve chain is ventral (Fig. 59). The digestive 
system is composed of the following parts : (i) fore-intestine, (2) mid-intestine, 
(3) hind-intestine, (4) salivary glands, (5) Malpighian tubules, and (6) 
accessory glands (Fig. 60). 



THE HEXAPODA: INSECTS 151 

FORE-INTESTINE: The fore-intestine begins at the rear of the buccal 
cavity. Its anterior end is a rather wide-open channel into which the food is 
passed after mastication. This leads directly into the pharynx, which, in 
mandibulatc insects, is a thin-walled tube. In insects with piercing mouth 
parts the pharynx is an organ of suction and is provided with powerful muscles. 
By the contraction of these muscles the pharynx acts as a pumping organ 
(Fig. 60). The pharynx leads into the esophagus, a thin-walled tube, which 
may terminate in a crop, followed by a proventriculus or gizzard. In most 
of the bloodsucking Diptera the gizzard is reduced to a valve that opens into 
the mid-intestine. In addition to these structures the esophagus may have one 




Fig. 60. Diagrammatic sectional view of the internal structures of a female mosquito. 
C, cardiac or csophageal valve; Cer, cercus; D, dorsal diverticula; E, esophagus; F, food 
channel; H, hind-intestine; M, Malpighian tubules; Ov, ovary; Ovi, oviduct; Ph, pharynx; 
Pph, pharyngcal pump; S, salivary duct; Sg, salivary glands; Sm, stomach; Sp, salivary 
pump; Spa, spermatheca; V, ventral diverticula of esophagus. 

to three diverticula or food reservoirs (Fig. 60), as they are called. These 
diverticula are very large in the mosquito but their exact function is not 
well known. 

THE MID-INTESTINE: The mid-intestine or stomach (Fig. 60) extends 
from the proventriculus to the insertion of the Malpighian tubules. It may be 
short and saclike or it may be long and coiled. It is in this portion of the 
alimentary tract that digestion and most of the absorption take place. The 
mid-intestine is joined, in many cases, to the fore-intestine by what has been 
termed the esophageal valve (Fig. 60 C). The esophageal valve is absent in 
the lice (Anoplura) and the bedbug. In many insects the food contained in 
the mid-gut is surrounded by a delicate membrane, the peritrophic membrane, 
which originates from a group of cells, the cardiac cells, located at the juncture 



152 MEDICAL ENTOMOLOGY 

of the epithelium of the fore- and mid-intestine. The peritrophic membrance is 
present in the majority of insects. 4 

THE HIND-INTESTINE: The origin of the hind-intestine is marked by 
the insertion of the Malpighian tubules. In many insects the hind-gut is 
divided into three fairly well defined regions the ileum, the colon, and the 
rectum (Fig. 61). 

STRUCTURE OF THE INTESTINE: The fore- and hind-intestine are 
of ectodermal origin. Internally each is lined with a thin intima, which is 
continuous with the cuticula of the body wall. The intima may be very thick 
as in the gizzard (proventriculus). Beneath the intima is a single layer of 
epithelial cells that is continuous with the epidermis. A basement membrane 
underlies the epithelial cells. The fore-intestine is surrounded by a layer of 
longitudinal muscle fibres overlaid by a thin band of circular muscle fibers. 
In the hind-intestine the muscle layers, from within, are first circular, then 
longitudinal, and usually again circular. The mid-intestine is of entodermal 
origin. It lacks the internal lining of intima and is composed of a single layer 
of epithelial cells resting on a basement membrane. It is surrounded by a layer 
of circular muscles overlaid by a thin sheet of longitudinal fibers. The entire 
intestine outside the muscle layers is surrounded by a thin sheet known as 
the peritoneal membrane. The peritoneal membrane may then be considered 
as the inner lining of the body cavity or hemocele. 

THE SALIVARY GLANDS: These are the most important glands con- 
nected with the fore-intestine, and they often play a significant role in the 
transmission of parasites (Figs. 60-62). The glands are paired structures and 
lie on each side of the intestine in the hemocele. Each gland consists of a 
cellular part and a duct that unites with its fellow from the opposite side to 
form a common salivary duct. The common duct opens at the base of the 
hypopharynx and, in some of the bloodsucking insects, extends throughout 
its length (Fig. 97) . These glands vary greatly in size and complexity. In the 
mosquito the glands are quite large and occupy a considerable space in the 
thorax. Each gland of the mosquito is trilobcd, with a central gland and two 
lateral glands (Fig. 62). The ducts of the three glands from each side unite 
into one, and this in turn joins its fellow from the opposite side to form a 
common salivary duct. At its point of entrance into the hypopharynx there 
is a muscular pump that forces the secretion into the wound made at the time 



4 Wigglcsworth (1930) states that it is absent in the Hemiptera, adult Lepidoptera, 
and some Coleoptera. 



THE HEXAPODA: INSECTS 




Fig. 61. (a) The digestive tract of the housefly with the main parts labeled. (I?) The 
salivary syringe to show details (highly magnified). A^ anal opening; F, fulcrum in head 
of fly; HI, hind-intestine; I, mid-intestine extending trom proventriculus (PR) to in- 
sertion of Malpighian tubules (T); M, muscles to syringe; O, esophagus; Od, esophageal 
diverticulum or crop; P, pharynx; PR, proventriculus; R, rectum; Sd, salivary duct lead- 
ing to hypopharynx from salivary syringe; Sga, salivary glands; Sp, salivary syringe; 
T, Malpighian tubules; V, valve to prevent backflow of salivary fluid. 



i 5 4 MEDICAL ENTOMOLOGY 

of obtaining blood. In many insects the salivary glands function for the secre- 
tion of silk, as in the caterpillars and the larvae of many Hymenoptera. 

The functions of the secretion of the salivary glands of bloodsucking in- 
sects are not well understood. It is known that in the mosquito the secretion is 
injected into the wound, causing the irritation and swelling. How this is 
brought about is not known. In some insects the secretion possesses an anti- 
coagulin (Anopheles rossi and A. jamesii), but in others such a function has 




Fig. 62. Left: The left half of the salivary gland of Anopheles punctipcnnis. Center: 
Cross section of the glands. Right: Cross section of a gland from Culcx pipicns showing 
masses of sporo/.oites of bird malaria. Cg, central gland; Lg, lateral gland; Sd, salivary 
duct. 

not been demonstrated. Metcalf (1945) has shown that the salivary glands of 
Anopheles quadrimaculatus contain an anticoagulin that is thermostable and 
active at dilutions of i :io,ooo; they also contain a powerful agglutinin for most 
vertebrate blood but not for chicken or turtle blood. Cornwall and Pattern 
have shown that the saliva of a muscid (Musca crassirostris) contains a power- 
ful anticoagulin, whereas Stomoxys calcitrant (the stable fly) has no anti- 
coagulin. Lester and Lloyd find that the salivary secretions of Glossina flies 
possess a powerful anticoagulin. Yorke and Macfie report that the salivary 
secretion of Anopheles maculipennis agglutinates red blood cells and also 



THE HEXAPODA: INSECTS 155 

possesses an anticoagulin and that the secretions of Culex pipiens and Aedes 
aegypti do not possess an agglutinin nor do they contain an anticoagulin. Mc- 
Kinlcy determined that an emulsion of the glands of Aedes aegypti, when 
injected intradermally, caused a severe itching and characteristic wheals on 
susceptible persons; it does not possess an anticoagulin nor does it hemolyze 
blood. It has also been shown that some species of horseflies (Tabanidae) 
possess an anticoagulin in their salivary glands. Puri has shown that the 
saliva of the bedbug causes the severe irritation and that it contains an 
anticoagulin. As bloodsucking insects must ingest their blood meal 
through a very minute channel, it would seem essential that some agent or 
agents be present to prevent the coagulation of the blood here or in the esoph- 
agus in order to allow it to flow freely into the mid-gut where digestion takes 
place. 

THE MALPIGHIAN TUBULES: The Malpighian tubules (Figs. 60,61) 
are usually elongated tubes that arise at the junction of the mid- and hind- 
intestine. In their origin they belong to the hind-gut. Their number varies 
but they generally occur in multiples of two, the usual number being four or 
six. In the Culicidac there are live, but most of the Diptera possess four. Each 
Malpighian tubule arises at the anterior end of the hind-gut and terminates 
blindly in the hcmocele. Though they are usually single, branching may occur 
or two may unite to form a common opening into the intestine (Fig. 61). In 
structure each tube is composed of a ring of epithelial cells surrounding a 
central channel. Each cell possesses a prominent nucleus, which may be much 
branched. The epithelial layer of cells rests on a basement membrane sur- 
rounded by a delicate peritoneal sheath. The function of these tubules is now 
generally regarded as excretory, extracting waste from the blood and storing it 
in the cells or passing it to the hind-intestine. The Malpighian tubules are of 
great interest to the parasitologist because within them certain parasites 
undergo part of their life cycles, for example, Dirofdaria immitis (Fig. 63), 
a rilarial roundworm infecting the dog. 

THE RESPIRATORY SYSTEM 

The respiratory system of insects consists of a paired series of tubes, tracheae, 
which, by branching, ramify through all parts of the body and its appendages. 
These tubes arise as invagi nations of the body wall and are usually located 
on the pleura of the second and third thoracic and first eight abdominal seg- 
ments (Fig. 42). The external openings are called spiracles, and the usual 
number is ten pairs. The spiracle is usually surrounded by a chitinous ring, 



156 MEDICAL ENTOMOLOGY 

the peritreme, and opens into an atrium or air chamber. From the air chamber 
extends a trachea, which branches and unites with its fellows to form longi- 
tudinal and transverse connections. From these main trunks innumerable 
branches extend to all the tissues and organs of the body. The spiracle, in its 
simplest form, consists of an opening to the exterior to admit air. There is, 
however, extreme variation in the structure of spiracles, and many possess a 
rather complicated apparatus for closure and for excluding dust, dirt, and 
moisture. In many insects a single spiracle may have several openings (Fig. 
194). The trachea consists of a tube lined internally with intima arranged in 
such a way that the thickenings form a spiral (Fig. 64). These spiral thicken- 
ings (taenidia) keep the trachea distended and allow the free passage of air. 




Fig. 63 (lejt). Malpighian tubule from Acdes vexans (a mosquito) containing three 
larval filarial worms, Dirofilaria immitis (dog filaria). These developed 17 days after the 
mosquito fed on the blood of a dog containing microfilaria. 

Fig. 64 (right). Small section of a trachea to show structure, e, epithelium; i, intima; 
t, taenidia. 

The tracheae finally terminate in tracheoles, which are the essential organs 
for respiration. The tracheoles are minute tubes that lack a chitinous lining and 
penetrate the various tissue cells to furnish the needed air. 

In addition to the respiratory system described above, various modifica- 
tions are found. In aquatic insects there may be tracheal gills, as in mosquito 
larvae (Fig. 105), and blood gills (which are rare), as in the larvae of some 
species of Chironomus and Simulium. 

In order to indicate the distribution of spiracles the following classification 
is much used (mostly applied to dipterous larvae) : 

1. Holopneustic Spiracles all open and arranged on thorax and first 7 or 8 ab- 

dominal segments. 

2. Hemipneustic One or more spiracles closed. 

(i) PeripneusticUsually spiracles of wing bearing segments closed. 



THE HEXAPODA: .INSECTS 157 

(2) Propneustic Only first pair of thoracic spiracles open. Example: pupae 

of mosquitoes. 

(3) Metapneustic Only the last pair of spiracles is open. This type is found in 

mosquito larvae, some parasitic larvae as Hypoderma spp. (warble 
flies), and others. 

(4) Amphipneustic The first and last pair of spiracles are open. Example: 

larvae of the Muscidae. 

THE BLOOD 

The blood is generally a colorless fluid that circulates freely in the hemocele, 
bathing directly all the internal organs and tissues. In some insects it may be 
colored from the absorbed food substances or may contain hemoglobin 
(rare) . In the plasma are found several types of leucocytes, but their functions 
are not well known. One type possesses a phagocytic function, and these cells 
undoubtedly play an important role. The blood is kept in circulation by a dorsal 
pumping organ, the heart. The heart is a tube that extends from near the 
caudal extremity to the head. It is usually closed at the posterior end and 
terminates in a nonpulsating anterior vessel, the aorta. In the heart there are 
paired ostioles or openings. The pulsations of the heart travel from behind 
forward so that the blood flows in at the ostioles and is then forced cephalad by 
the wavelike muscular contractions, being discharged through the aorta. The 
ostioles are so constructed that they admit the entry of the blood, but as the 
contraction waves passes forward, backflow in the heart itself and to the hemo- 
cele is prevented. 

THE MUSCULAR SYSTEM 

The muscles of insects are all internal. The body wall and various invagina- 
tions (apodemes, furca, etc.) furnish the points of origin, and the insertion 
points are those portions or parts of the body to be moved. As a rule, insect 
muscles are composed of numerous fibers enclosed in sheaths and appear 
almost colorless, transparent, or yellowish white; they are soft and gelatinous. 
The number of muscles is large and their arrangement very complicated. In 
their histological structure all the muscle fibers are cross-striated and present 
a beautiful appearance to the microscopist. To the parasitologist and medical 
entomologist the normal histology is of considerable significance, for in some 
muscle tissues certain Nematodes pass part of their life cycle (Wuchereria 
bancrofti, in the thoracic muscles of the mosquitoes; Loa loa in similar muscles 
of Tabanidae) . 



i 5 8 



MEDICAL ENTOMOLOGY 



THE REPRODUCTIVE SYSTEM 

In practically all insects the sexes are distinct. The female reproductive 
organs (Fig. 65) consist of the ovaries, paired structures; each ovary is com- 
posed of a variable number of egg tubes or ovarioles; the ovarioles from each 
side open into an oviduct; the oviducts unite to form a common duct, the 
vagina, which opens to the exterior ventral of the anal opening. Attached 
to the vagina and opening into it are usually found a pair of accessory glands 




Fig. 65. Female reproductive system of Anopheles punctipcnnis. Ag, accessory gland; 
Ov, ovary; Ovd, oviduct; Sp. spcrmatheca; V, vagina. 

and a pouch (there may be several), the spermatheca, for the 'reception and 
storage of the sperm. As the majority of insects probably mate but once, and 
the female oviposits over a long period of time, it is essential that a storage 
place be provided for the sperm. 

The male reproductive organs consist of a pair of testes composed of 
testicular follicles; from each testis extends a canal, the vas deferens, which 
unites near the exterior with its fellow to form the ejaculatory duct. Usually 
each vas deferens is enlarged along its course to form a sac, the vesicula 



THE HEX APOD A: INSECTS 159 

seminalis, in which the spermatozoa congregate. There is also generally a 
pair of accessory glands. The ejaculatory duct, at its terminal section, is enclosed 
in a chitinous tube that forms the intromittent organ or aedeagus. The aedeagus 
or penis is a variable structure, and around it often develop a most com- 
plicated grouping of clasping and holding organs. 

THE METAMORPHOSIS OF INSECTS 

The great majority of insects, in the course of their postembryonic develop- 
ment, undergo remarkable changes in form or metamorphosis; the beautiful 
butterfly was once a caterpillar; the May beetle, a grub; the housefly, a footless 
maggot. The most obvious changes are external, though the internal meta- 
morphosis is even more complicated and as yet not well understood. Practically 
all insects lay eggs and these develop externally to the mother. In some insects 
the embryonic development may be completed before the egg is laid, as in 
many plant lice and flesh flies; the egg may hatch and the larva develop in a 
uteri nelike cavity in the mother, as in the Glossina flies, the sheep tick or ked, 
and all the Piipipara; or partial embryonic development may take place before 
egg laying, as in the bedbug. There are two general types of postembryonic 
development incomplete metamorphosis (hemimetabolous), and complete 
metamorphosis (holometabolous). Those insects that do not undergo changes 
in form during growth are called ametabolous (these include the two primitive 
orders, Thysanura and Collembola). 

THE EGG: The eggs of insects vary greatly in their shape, size, and mark- 
ings. Attention here is directed only to the eggs of those insects that are 
annoying to man or his domestic animals. These eggs all possess a distinct shell 
and arc laid on or near the food on which the young are to feed. The egg of the 
bedbug (Fig. 71) is quite large and distinctive; that of the louse is attached 
to hairs or clothing and possesses a structure for attachment (Fig. 81); the 
housefly deposits large, smooth, white eggs (Fig. 173). Frequently the most 
distinguishing characteristic of the eggs of certain insects is the manner of 
oviposition. Thus the mosquito, (Culex spp., lays its eggs in rafts (Fig. in) 
on the surface of the water; horseflies (Tabanidae) deposit their eggs in 
masses glued to the leaves or stems of aquatic or semiaquatic plants (Fig. 158). 

The young larva escapes from the egg either by breaking the shell with 
its mandibles or mouth hooks, by pushing off a cap by means of an air cushion 
(lice); or by breaking the shell with a special apparatus known as an egg 
burster or hatching spines. Such hatching spines are easily seen on the dorsal 
surface of the head of the first-stage mosquito larva. 



160 MEDICAL ENTOMOLOGY 

INSECTS WITH INCOMPLETE METAMORPHOSIS: The most 
striking feature of this type of metamorphosis is the development of wings as 
external outgrowths of the mesothoracic and metathoracic segments. In all 
other respects except in size and the rudimentary condition of the genital 
appendages, the young (generally called nymphs) resemble the adults. A good 
example is a grasshopper or a bug. Furthermore in this type of metamorphosis 
the life of the young and of the adult is essentially the same: they live in the 
same situation and feed on the same food. 5 The adults are provided with wings 
giving them increased power of locomotion. The power of flight gives them 
a wider feeding range and provides for the more rapid spread of the species 
and more successful mating. 

INSECTS WITH COMPLETE METAMORPHOSIS: In this group the 
young and adults are totally unlike in appearance. Familiar examples are 
the caterpillars, which develop into moths or butterflies; maggots, which 
later become flies; and grubs, which transform to beetles. The young stage 
is generally known as the larva. When the larva has reached maturity, it 
ceases to feed and proceeds to undergo a most remarkable change. It now 
either spins a silken cocoon (most moths), forms a cell in the ground (many 
beetles), seeks out some sheltered place, uses the last larval skin as a shelter 
(many Diptera), attaches itself to some support (butterflies and some beetles), 
or in other ways makes provision for the changes that are to follow. The 
last larval skin is now cast ofT (except in many Diptera), and a new stage, the 
pupa, appears (Fig. 103). Within the pupa many of the larval tissues are 
broken down and rebuilt to form the adult. From the pupal skin emerges an 
entirely new form, the adult. 

The most striking characteristics of this type of metamorphosis are: (i) the 
larval stage occupies an entirely different habitat and requires different food 
from that of the adult; (2) the wings are developed internally during the 
larval period and only appear externally as wing pads (Fig. 103) in the pupal 
stage; and (3) a resting stage appears, the pupa, within which the larval tissues 
are broken down and the adult is rebuilt from histoblasts or embryonic tissues. 

GROWTH IN INSECTS 

The growth period in insects is restricted to the nymphal or larval stage. 
Growth in the nymphal and larval stages is accomplished by a periodic shed- 

5 This last statement does not apply to three orders, the May flies, stone flies, and the 
dragonflies, whose nymphs are aquatic and adults aerial. Comstock has designated this 
type as incomplete or hemimetabolous, and the type represented by the Orthoptera, 
Hemiptera, Anoplura, etc., as paurometabolous or gradual metamorphosis. 



THE HEXAPODA: INSECTS 161 

ding of the skin, molting. As the skeleton is external, no increase in size beyond 
a certain expansion can take place after the cuticula has hardened. This dif- 
ficulty is overcome by molting. When a larval stage has reached its full growth, 
the cuticula splits at some convenient place and a new larva crawls out pro- 
vided with a soft external skin capable of considerable extension. The new 
cuticula is laid down beneath the old before the latter is shed. Molting takes 
place at regular intervals and the number of molts varies in different groups 
of insects. In the mosquito the larva molts four times before the pupal stage 
is reached; in most of the higher Diptera only three molts occur; in the beetles 
and moths five or more may occur; in other groups three to many molts may 
take place. 6 During the larval growth large quantities of food are stored up as 
fat. This food supply is largely used up during the pupal period, being em- 
ployed in the development of the tissues of the adult. 

The adult, though it feeds, does not increase in size. Molting does not occur, 
and, once the external skeleton is fully hardened, no great expansion of body 
size is possible. Food is now taken to provide for the adult activities and the 
development of eggs and sperm. In many insects the adults do not feed but 
depend on the store of food carried over from the larvae. 

SYNOPSIS OF INSECT CLASSIFICATION 

The Hexapoda or insects constitute an immense assemblage of species; 
probably more than 800,000 species have already been described, and new 
ones are constantly being discovered. The class is divided into two subclasses, 
the Apterygota and Pterygota. The Apterygota contain the wingless, primi- 
tive insects, and these are included in two orders, the Thysanura and the 
Collembola. The Pterygota include all the other insects whether wingless or 
not. The wingless condition of the forms included here is not a primitive 
one but acquired. The Pterygota are divided into a number of orders but rarely 
do workers agree as to the exact number or their arrangement. It is proposed 
here to give a brief synopsis of only those orders that contain important species 
annoying to man or his animals. 7 These include only eight or nine of the 
twenty to nearly forty orders now recognized. Of these orders the most im- 
portant are the Hemiptera, the Anoplura, the Diptera, and the Siphonaptera. 
The other orders, the Orthoptera, Lepidoptera, Coleoptera, and Hymenoptera, 
contain forms that may act as mechanical carriers of disease organisms 



6 The intervals between molts or ecdyses are called stadia; the form of the larva or 
nymph during a stadium is called an instar. 

7 For a full account the reader is referred to works by Comstock, Sharp, Imms, Kellogg, 
Brues and Melander, and Matheson, all indicated in the References. 



162 MEDICAL ENTOMOLOGY 

(Orthoptera), produce diseased conditions by their poisonous hairs (Lepidop- 
tera) or stings (Hymenoptera), cause ill effects by their vesicating substances 
(cantharidin of blister beetles), or serve as intermediate hosts of helminths 
(Coleoptera, Orthoptera, etc.). It is not proposed to treat these four orders 
in any detail, but they are discussed briefly in the last chapter and mentioned 
in a few other places. The following simple key will serve to place those 
insects that are of great importance to man: 

KEY TO THE PRINCIPAL ORDERS OF INSECTS (ADULTS) 
OF MEDICAL IMPORTANCE 

1. Wingless insects 2 

Winged insects 9 

2. Free-living forms, not parasitic 3 

Not free-living, ectoparasites 5 

3. Abdomen sharply constricted at base; cerci absent Hymenoptera 

Abdomen not sharply constricted at base, broadly joined to the thorax; 

cerci present or absent 4 

4. Mouth parts fitted for biting; flattened insects; body without scales. 

(Many cockroaches) Orthoptera 

Mouth parts consisting of a proboscis coiled up beneath the head; body 
usually covered with scales or long hairs. (Wingless moths) Lepidoptera 

5. Mouth parts formed for piercing and sucking 6 

Mouth parts adapted for biting. (Biting lice) . (Mallophaga) Anopltira 

6. Body strongly compressed (flattened from side to side) ; antennae in 

grooves visible from above; legs fitted for jumping or running. 

(Fleas) Siphonaptcra 

Body not compressed but may be flattened from above down; antennae 
not in grooves, visible or not from dorsal surface 7 

7. Antennae short, located in pits and not visible from dorsal surface. 

(Louse flies; Pupipara) Diptera 

Antennae fully exposed 8 

8. Tarsus with one claw and fitted for clinging to hairs. (Sucking lice; 

Siphunculata) Anoplura 

Tarsus with two claws and not adapted for clinging to hairs . . Hemiptera 

9. With a single pair of membranous wings; hind pair represented by 

short processes (halteres or balancers) Diptera 

With two pairs of wings 10 

10. The two pairs of wings unlike in structure or texture n 

The two pairs of wings similar in structure or texture 13 



THE HEXAPODA: INSECTS 163 

11. The front wings hard and horny, shell-like, and without distinct vena- 

tion. Hind wings thin and membranous; mouth parts for chewing. 

(Beetles) Coleoptera 

The front wings not as described above 12 

12. The front wings parchmentlike with a network of veins; hind wings 

folded fanlike beneath the front wings; mouth parts for chewing 

Orthoptera 

The front wings leathery at base and membranous on apical portion 

(Fig. 68) ; mouth parts fitted for piercing and sucking 

(Heteroptera) Hemiptera 

13. Wings covered more or less densely with scales; mouth parts fitted for 

sucking and, when at rest, coiled up under the head Lepidoptera 

Wings not covered with scales; mouth parts fitted for biting or sucking 
but never coiled up under head 14 

14. Mouth parts enclosed in a jointed beak and fitted for piercing and 

sucking; they are located at the posterior part of the head, just in 

front of the first pair of coxae (Homoptera) Hemiptera 

Mouth parts not enclosed in a jointed beak; in normal position 

Hymenoptera 

REFERENCES 

**Berlcsc, Antonio. Gii insetti; loro organizzazione, sviluppo, abitudini e rap- 

porti coU'uomo. Milan, 1909. 

Brues, C. T., and Melander, A. L. Key to the families of North American in- 
sects. 1915. 
, and Melander, A. L. Classification of insects. Bull. Mus. Comp. Zool., 

Harvard Univ., 1932. 

**Carpentcr, G. H. The biology of insects. London, 1928. 
*Comstock, J. H. An introduction to entomology. Ithaca, N.Y., 1947. 

. The wings of insects. Ithaca, N.Y., 1918. 

Cornwall, J. W., and Patton, W. S. Some observations on the salivary secretion 

of the common blood-sucking insects and ticks. Ind. Jl. Med. Res., 2: 569-593, 

1914. 

**Costa-Lima, A. da. Insetos do Brasil. 1939-1945. 5 vols. 
**Essig, E. O. College entomology. New York, 1942. 
**Folsom, J. W., and Wardle, R. A. Entomology with special reference to its 

ecological aspects. 4th ed. Philadelphia, 1934. 
Graham-Smith, G. S. Further observations on the anatomy of the proboscis of the 

blow-fly, Calliphora erythrocephala L. Parasitology, 22: 47-114, 1930. 
Henneguy, L. F. Les Insectes. Paris, 1904. 



164 MEDICAL ENTOMOLOGY 

*Imms, A. D. A general textbook of entomology. 3rd ed. London, 1934. 
Lester, H. M. O., and Lloyd, L. Notes on the process of digestion in tsetse-flies. 

Bull. Ent. Res., 19: 39-60, 1928. 
McKinley, E. B. The salivary gland poison of the Aedes (argenteus) aegypti. 

Proc. Soc. Exp. Biol. Med., 26: 806-809, 1929. 

**Matheson, R. Entomology for introductory courses. Ithaca, N.Y., 1947. 
Maxwell-Lefroy, H., and Howlett, P.M. Indian insect life. Calcutta, 1909. 
Packard, A. S. A textbook of entomology. New York, 1898. 
Patton, W. S., and Cragg, F. W. A textbook of medical entomology. London, 

*9*3- 

, and Evans, A. M. Insects, ticks, mites, and venomous animals of medical 

and veterinary importance. Part I. Medical. Croydon, England, 1929. 

Puri, I. M. Studies on the anatomy of Cimcx lectularius. Parasitology, 16: 84-97, 
269-278, 1924. 

**Schroeder, Chr. (editor). Handbuch der Entomologie. Jena, 1928, 1929. 2 
vols. 

Sharp, David. Insects. In Cambridge Natural History, vols. V and VI. Lon- 
don, 1895, 1899. 

**Snodgrass, R. E. Principles of insect morphology. New York, 1935. 

Tillyard, R. J. The insects of Australia and New Zealand. Sydney, 1926. 

Wigglesworth, V. B. The formation of the peritrophic membrane in insects, with 
special reference to the larvae of mosquitoes. Quart. Jl. Micros. Sci., 73: 593 
616, 1930. 

. The principles of insect physiology. New York, 1939. 

Yorke, W., and Macfie, J. W. S. The action of the salivary secretion of mos- 
quitoes and of Glossina tachinoidcs on human blood. Ann. Trop. Med. Parasit., 
18: 103-108, 1924. 



CHAPTER VI 



The Orders Orthoptera 
and Hemiptera 



'"THHE order Orthoptera includes such insects as cockroaches, grasshoppers, 
-L crickets, and related groups. They possess chewing mouth parts (Fig. 45) 
and normally two pairs of wings, of which the outer (tegmina) pair is more 
or less parchmentlike with distinct veins; the lower or hind wings are thin 
and folded fanlike when at rest. Metamorphosis is gradual. Though the order 
contains many species that are destructive to vegetation (practically all are 
vegetarians), only a single family is of interest here. 

THE FAMILY BLATTIDAE THE COCKROACHES 

Cockroaches are primarily inhabitants of the tropical and subtropical re- 
gions. They are easily recognized by their oval, flattened bodies; long, filiform 
antennae; and legs fitted for running or walking. The head is almost concealed 
by the prothorax and is bent downward so that the mouth parts project be- 
tween the first pair of legs. Most of the species live in the wild in their natural 
habitats. At least four species, however, have become largely domesticated and 
have invaded our homes, restaurants, hotels, food-storage warehouses, commer- 
cial establishments of all kinds, and similar places where food and warmth 
are available. These species are all voracious feeders, attacking almost any 
vegetable or animal matter. They are largely nocturnal in activity, and warm 
kitchens, laundries, bakehouses, restaurants, and hotels are their favorite 
haunts. Unlike most insects the females produce special egg cases within their 
genital armature. When ready for egg laying the female excretes a special 
substance that forms an egg case (ootheca) composed of two parallel rows. 
As each egg sac is formed, an egg is passed into it either from the right or left 
ovary. This continues till a purselike capsule is completed. It may be seen ex- 
tending from the end of the abdomen when it is about ready to be dropped. 



r66 MEDICAL ENTOMOLOGY 

Each species produces its own type of ootheca (Fig. 66). The oothecae are 
dropped at convenient places, and the eggs normally hatch in a month or two. 
The female may carry the egg case till the eggs are ready to hatch as in the 
case of the German roach (Blatella germanica). 



Fig. 66. Egg case of Blatta orientdis. 

The four common, more or less domesticated species (Fig. 67) are Blatella 
germanica (the German roach or croton bug), Blatta orientalis Linn, (the 
oriental roach), Periplaneta amencana Linn, (the American roach), and 
Periplaneta australasiae Fabr. (the Australian roach). Another species, the 
brown-banded roach (Supella supellectilium Serv.), has become established 
in the southern United States and to some extent in the North. These species 
may be recognized by the aid of the following key (adults) : 

1. Tegmina in male not reaching the end of the abdomen, covering only 

about two-thirds of it; in female tegmina represented by small pads. 
Length about i inch. Almost black without any markings (Fig. 67) . . 

Blatta orientalis 

Tegmina in both males and females reaching or extending beyond the 
end of abdomen; if not covering the abdomen then marked with two 
light bands, one at base of wings and another about one-third of length 
from base 2 

2. Length of insect rarely more than % inch 3 

Length more than i inch 4 

3. Color uniformly pale brown with two parallel dark stripes on pro- 

notum (Fig. 67) Blatella germanica 

Color uniformly dark brown with two pale bands near the base of teg- 
mina, one at base and another a third of the length from the base 

Supella supellectilium 

4. Thorax yellow with two large blotches of chestnut brown; tegmina lack- 

ing a yellow submarginal stripe along basal third. Length from i% to 

2 inches (Fig. 67) Periplaneta amencana 

Thorax yellow, with base and one or two central spots black; tegmina 
with a pale-yellow, submarginal stripe along basal third. Length about 
i inch Periplaneta australasiae 

The German roach or croton bug (Blatella germanica) is the smallest house- 
hold roach. It is world-wide in distribution and the commonest species in 



ORTHOPTERA AND HEMIPTERA 




rig. 67. Cockroaches. (/) Blatta oncntalis (female), (j) Blatta oricntahs (male), (j) 
Blattella germanica (female). (4) Preiplaneta americana (male). (From British Museum, 
after Laing.) 

homes, restaurants, hotels, and similar places. The developmental period from 
the hatching of the eggs to the adult stage is from three to four months; the 
adults live from six to ten months. The American roach (Periplaneta ameri- 
cana) requires nearly a year to complete its developmental cycle though this var- 
ies greatly. The adults live a year or more. This roach is common on board ships 
and in warehouses, sugar refineries, meat-packing establishments, zoological 



168 MEDICAL ENTOMOLOGY 

gardens, city dumps, and similar places. In America it commonly invades our 
homes. Gould and Deay (1940) describe migrations of this species from place 
to place in the North. In the South along the Gulf coast it is common in palm 
trees, and nightly flights take place. It is known to be able to make long flights. 
The oriental roach (Blatta orientalis) is almost jet black in color and is 
primarily a house pest, preferring dark, warm basements, kitchens, and similar 
places. If food and favorable conditions of warmth and moisture are available, 
the developmental cycle from egg to adult requires nearly a year. The Aus- 
tralian roach (Periplaneta australasiae) is somewhat smaller than the Ameri- 
can roach and is easily recognized by the pale-yellow streak on the tegmina. 
It is said not to be common in houses but prefers greenhouses and such places. 
In addition, many other roaches occur in tropical and subtropical regions, 
and some of these may be distributed by commerce and adapt themselves to 
our homes and warm buildings. In recent years the brown-banded roach 
(Supella supellectilium Serv.) has spread into many parts of the United States 
and has become a house pest, especially in cities. It occurs as far north as 
Massachusetts, Wisconsin, South Dakota, and central California. Unlike 
other roaches this gregarious species prefers cupboards, shelves in closets, 
behind pictures and moldings, desks, and such places. 

COCKROACHES AND HUMAN DISEASE: On account of their om- 
nivorous and filthy habits and close association with man, cockroaches have 
long been suspected of disseminating pathogenic organisms. As they feed 
on man's food and his fecal wastes, roam at will through his household, and 
invade food shops, bakeries, meat-packing and food-storage plants, and similar 
places, it would be surprising if they did not distribute all kinds of organisms 
that are capable of surviving passage through their intestines or carriage on 
their bodies. Although various authorities have shown that viable bacteria 
can pass through the intestines of roaches and be carried on their bodies, yet 
nothing has been established of the importance of roaches in disease dissemina- 
tion. Barber (1914) demonstrated that viable organisms of cholera pass through 
the intestines, but there are many other methods of dissemination of much 
greater significance. This is true also of such diseases as tuberculosis, typhoid, 
leprosy, and dysenteries, the etiological agents of which can survive passage 
through their intestines and be carried on their bodies. Such protozoan cysts 
as those of Endamoeba histolytica, Endamoeba colt, and Giardia intestinalis, 
survive and this may be of some significance. Investigations in Peru demon- 
strated that 7 per cent of the house-infecting cockroaches were carriers of 
viable cysts of Endamoeba histolytica (Schneider and Schields). As intermedi- 
ate hosts of helminths they are of considerable importance. All four common 



ORTHOPTERA AND HEMIPTERA 169 

cockroaches serve as intermediate hosts of the roundworms, Gonglyonema pul- 
chrum (which is reported from rats and man), G. neoplasticum (which pro- 
duces a carcinoma in the stomach of rats; not reported from man), G. orientate 
(a parasite of rats), and the acanthocephalid, Monilijormis monilijormis (a 
parasite of rats and occasionally of man) . 

CONTROL OF COCKROACHES : As roaches are lovers of filth and prefer 
darkened corners, cracks, and out-of-the-way places, the first procedure is a 
thorough clean-up and the destruction of all wastes. When this has been done, 
an application of sodium fluoride is one of the most effective methods of con- 
trol. Commercial sodium fluoride, either pure or diluted with a carrier such as 
ground gypsum, chalk, or other diluent to give 50 per cent sodium fluoride, 
dusted or blown into all cracks, crevices, and runways and about sinks, tables, 
shelves, or other hiding places will quickly kill roaches. As the roaches run 
over the powder, it sticks to their bodies and in cleaning themselves they 
ingest the material, which proves a prompt poison. Of course, sodium fluoride 
should not be used near food or where there is a possibility of contaminating 
food. One treatment should be allowed to remain for several days, and the 
application is best made during the evening hours. The exposed dust should 
be cleaned up, but all in the cracks, crevices, and similar places should be 
allowed to remain since the powder remains effective almost indefinitely. This 
treatment should be repeated if all roaches are not destroyed by the first 
application. 

Phosphorous pastes are purchasable and are quite effective. Smear the paste 
inside cardboard rolls and place them in the runways of the roaches. The 
pastes are particularly valuable in very damp climates because powders may 
harden and not be effective. 

DDT as a powder or as a spray is very effective if properly and thoroughly 
applied. The dust should contain from 10 to 20 per cent of DDT, and all 
cracks, crevices, areas behind objects, baseboards, and runways should be 
liberally covered with the mixture. The visible dust may be removed in a 
few days but not that from the cracks and crevices. The application should 
be repeated in about five or six weeks to kill any young that may have hatched 
from eggs. A 5 per cent DDT oil spray is also effective but usually slower in 
action. Spray thoroughly and heavily with 5 per cent DDT in refined kero- 
sene oil or as a 5 per cent emulsion. Carefully apply to all cracks, crevices, 
under draining boards, about sinks, on all runways, behind baseboards, and 
in similar places. Avoid contaminating food. The residual effect of the DDT 
will act for a considerable time. 

Probably the most effective insecticide for the control of cockroaches is the 



170 MEDICAL ENTOMOLOGY 

recently developed commercial product known as chlordane. This material 
can be obtained from dealers, and full directions for its use will be found 
on the containers. Normally a 2 per cent solution is most effective. A com- 
bination spray containing 5 per cent DDT and 2 per cent chlordane is now 
on the market and is used as directed by the manufacturers. 

THE ORDER HEMIPTERA: SUBORDER HETEROPTERA 

The True Bugs 

IThe order Hemiptera consists of two suborders, the Heteroptera and 
Homoptera. The Homoptera contain no insects known to be of medical 
importance. They are all primarily vegetarians sucking the sap from plants 




Fig. 68. Some hemelytra of the Heteroptera. (A) Diagrammatic illustration of 
hemelytra with the areas labeled. (B) Hemelytron of an Anthocoridae (Triphleps). (C) 
Hemelytron of a Coreidae (Leptocoris) . (D) Hemelytron of a Miridae (Poecilocapsus). 
c, cuneus; cl, clavus; co, corium; e, emboliurn; m, membrane. (Modified from Comstock.) 

of all kinds.lThe Heteroptera are also mainly vegetarians, but a few families 
are predaceous, sucking the blood of other insects or attacking animals in- 
cluding man. Their chief characteristics are the possession of two pairs of 
wings (except the wingless forms) : the fore wings are thickened at their 
bases (Fig. 68), and the membranous extremities overlap on the back; the 
hind wings are thin with few veins. The mouth parts consist of a jointed beak 
(Fig. 46) which contains the piercing and sucking organs; the beak arises 
from the front part of the head. The metamorphosis is graduafl 

The true bugs are abundant in species and individuals. Many species are 
very injurious to plants on account of their habit of piercing and sucking the 
sap; some are beneficial as they feed on noxious insects. t)nly two families 
contain species that are known to be injurious to man as bloodsuckers and 
as carriers and intermediate hosts of pathogenic organism^ Other families 
have certain species that may occasionally attack manjand a list of these is 



ORTHOPTERA AND HEMIPTERA 171 

given at the end of this chapter. The following brief key will aid in recogniz- 
ing the principal families that may be noxious to man: 

KEY TO THE FAMILIES OF THE HETEROPTERA 
RECORDED AS BITING MAN 

1. Antennae shorter than the head and concealed in depressions on the 

underside of the head beneath the eyes. All forms aquatic 2 

Antennae as long as or longer than the head and fully exposed 3 

2. Hind tarsi consisting of two segments, the last bearing two distinct claws; 

large flattened bugs. Fore wing with the membranous portion with 

distinct veins. (The giant water bugs; Fig. 75) Belostomatidae 

Hind tarsi consisting of three segments, the first very short and indis- 
tinct; tarsal claws setiform; head deeply inserted into prothorax. (Boat- 
shaped bugs, the back swimmers) Notonectidae 

3. Beak composed of three segments 4 

Beak composed of four sfg ments 6 

4. Beak stout, lying in j cross-striated groove hut not reaching the middle 

coxae; ocelli, whe n present, placed distinctly behina ihe eyes or behind 

a transverse dtfp ress i on . (Th e assassin bugs) Reduyiidae 

Beak elongate^ extending to middle coxae and groove not cross-striateu',' 

ocelli, wh:, n p rcse nt, not placed as above 5 

5- Ocelli abse nt . f ore w i n g s reduced, without membrane or vestigial. (The 

bedbug*) Cimicidae 

Ocelli Present; fore wings usually well developed; embolium present 

(Fi?. 68). Membrane of fore wings veinless or with indistinct veins. 

(*\owcr bugs) Anthocoridae 

6. Fron t j e g s fi ttec l f or seizing prey; fore tibiae and usually the front femora 

ar med with stout spines which interlock Nabidae 

F roi it legs fitted for walking, normal 7 

7. Fror, t w j n g w ith a V-shaped portion (cuneus) at the apex of the hard- 

ef d base of the wing (Fig. 68) ; membrane with one or two closed 

>. (Leaf bugs) Miridae 

wings not as described above 8 

absent. (Cotton stainers) Pyrochorridae 

present; no transverse depression in front of the ocelli 9 

rane of fore wing with five simple veins arising from its base. 

nch bugs) Lygaeidae 

ane of fore wing with many, usually anastomosing, veins arising 
transverse basal vein. (Squash bugs) Corcidae 



1^2 MEDICAL ENTOMOLOGY 

THE FAMILY CIMICIDAE THE BEDBUGS 

This is the well-known bedbug family. The most distinctive features are 
the depressed bodies, fitting them for creeping into cracks and crevices; the 
absence of wings except for the small padlike elytra (remnants of the fore 
wings, Fig. 69); the beak is segmented and lies in a groove on the ventral 
surface of the head and thorax; the head is short and broad and bears a pair 
of prominent compound eyes; the ocelli are absent; the antennae are four 
segmented | 

| The family contains three principal genera, Cimex, Oeciacus, and Haema- 
tosiphom (Some five or six others have been described.) The entire family con- 
tains not over 35 well-defined species. 

j| THE GEN,JJS CIMEX: Several species have been described as belonging 
to this genus.AOnly two of them are consistent parasites of man. The common 
bedbug, Cimex lectularius Linn., and the tropical bedbug, Cimex hemipterus 
Fabr., are persistent invaders of huma^ nabitJ^ ons anc ^ ^ ve primarily on 
human blood|though they readiVy teed on rabbits, m\ ce wmte rats > an d fowls. 
\Cimex lectularius Linn, (the bedbug, wall louse, maVg an y flat > etc -) is tne 
common bedbug (Fig. 69) of the temperate zones. Its bodv is flattened dorso- 
ver^aiiy and is well adapted to its mode of life. The adult mt asures 4 to 5 mm - 
in length and about 3 mm. in width. It is reddish brown in c olor - The head 
is broad and flat and fits rather neatly into the deeply concave ai lterior P art of 
the prothorax. The antennae are four-segmented; the last two segments are 
elongate and much thinner than the precedindJThe eyes are pro, minent ancl 
deeply pigmented. The beak is three-segmented and lies in a groove reacn , in g 
the middle coxaej The mouth parts are fully explained on_pages 130-^ J^ne 
thorax appears as a single segment, the large anterior part being the pr otn r a x- 
Dorsally the mesothorax may be distinguished by the attachment of the i ecluced 
fore wings. The metathorax lies beneath and behind the fore win^ Sl The 
abdomen consists of eight visible segments; the terminal ones (the ni uh and 
tenth) are modified for sexual purposes|((Fig. 70) . 

A great many insects possess a distinctive odor, and this is especi true 
of bedbugs, the "bedbuggy" odor of infested dwellings being very '' ecl 
and easily recognized by anyone familiar with it. (The odor of the 1 
produced by special stink glands, which, in the nymphs, open on t 
surface of the abdomen and on the ventral side of the last thoracic f 

of the adult. Puri has described these glands in great detail; he cons r 

function to be defensive and sexual, 
The males and females of bedbugs can be recognized easily. Ir ie 



ORTHOPTERA AND HEMIPTERA 173 

(Fig. 70) the abdomen gradually narrows from the third segment to the 
rather pointed tip, where are located the genitalia. In the female the abdomen 
does not narrow so much, and the tip is broadly rounded (Fig. 70). The 
external genital organ of the male consists of a sclerotized, sharply pointed 
aedeagus, which arises from the interior of the ninth segment. It is directed 
to the left side (seen from the dorsal surface). When not extended it lies in 
a groove of the segment. The aedeagus is grooved on its inner face, and at its 




I'ig. (>(). The bedbug, Cimcx lectularms. Female. (Courtesy De- 
partment of Agriculture, Division of Entomology, Canada.) 

base lies the penis. The anal opening is in front of the tenth segment, which 
appears to surround i Jjln the female the external genital organs consist of the 
genital opening surrounded and supported by sclerotized plates or gona- 
pophyses. On the ventral surface of the abdomen of the female there is a 
rather sharp and deep depression or slit on the posterior margin of the fourth 1 
segment, about halfway between the median line and the margin. This leads 
to a peculiar organ known as the organ of Berlese. It is through this organ 
that the male fertilizes the female, the sperm being introduced into it and 
not into the genital opening at the time of copulation/ In mating the male 

1 In reality the fifth segment as the first visible abdominal segment is the second. 



174 MEDICAL ENTOMOLOGY 

inserts the aedeagus into the slit, the penis passes down the groove and ejects 
the sperm into the opening of the organ of Berlese. 

1 BIONOMICS: Bedbugs are primarily parasites of man, though they feed on 
fowls, mice, and white rats and are frequently serious pests of rabbits in rab- 




Fig. jo. Clmcx lectulanus. Upper: Tip of abdomen of male (ventral view) . Lower: Tip 
of the abdomen of female (ventral view). AD, aedeagus; AO, anal opening; CA, cauda; 
G, groove in aedeagus along which penis moves in act of copulation; GO, genital opening 
guarded by two pairs of gonopophyses; GP VIII and GP IX, gonopophyses of the eighth 
and ninth segments; GR, groove in the ninth segment for the reception of the aedeagus; 
P, hairy process of the ninth segment; SP, spiracle; VIII, IX, X, eighth, ninth, and tenth 
segments. 

bitries. They are nocturnal in their feeding habits and during the day hide 
in convenient cracks, crevices, or other hiding places in sleeping rooms; under 
loosened wallpaper and moldings; in cracks in the flooring, old wooden 
bedsteads, and the creases and folds of mattresses; under bedding; and in 
places where mice, white rats, or rabbits are reared. As they are gregarious, 



ORTHOPTERA AND HEMIPTERA 175 

large numbers may be found in infested rooms. Mating takes place at irregular 
intervals, and the eggs are laid in the hiding places of the bugs. The egg (Fig. 
71) when laid is pearly white, gradually changing to a yellowish white. It 
measures 1.02 mm. in length by 0.44 mm. in width. The shell is distinctly 
reticulated and has a cap or lid that is pushed off when the nymph emerges. 
Each female is capable of laying from 75 to 200 eggs. Titschack records a single 
female that laid 541 eggs. The eggs are not all laid at one time but usually in 
ones, twos, threes, or small batches each day. Cragg records that a caged 
female, when supplied with food and its mate, laid 174 eggs in 105 days and 





Fig. ji (Icjt). The egg of the bedbug, Cimex lectularius. 

Fig. 72 (right). A large reduviid bug from South America, Pangstrongylus (Triatoma) 
me gist us. 

only ceased laying at the approach of cold weather. The adults live a long time, 
at least six or seven months to a year. They can also withstand long periods 
of starvation, especially during cold weather when they become inactive. 
Adults have been kept alive without food for a year, and the nymphs can 
withstand varying periods of starvation, 70 days or moreJ 

JLiFE HISTORY: The egg hatches in from six to seven days (longer if the 
temperature is low) . The first-stage nymph is very active and closely resembles 
the adult except in size. It will feed rather promptly. After feeding, the nymph 
hides in some convenient place to digest its blood meal and prepares to molt 
to the second instar. There are five molts, and the nymph takes, practically 
always, only a single blood meal between molts. According to Jones, the 
development period from egg to adult is a little over 30 days (the experi- 



176 MEDICAL ENTOMOLOGY 

ments were carried out at a temperature of 27 C. and a relative humidity of 
75 per cent; the nymphs were fed to repletion between each molt). He found 
the length of the instars to be: first instar, 5 days; second, 4.5 days; third, 4.2 
days; fourth, 4.6 days; and the fifth, 6 days. The nymphal life may be greatly 
prolonged by low temperatures, lack of food, or other factors affecting de- 
velopment. Both the nymphs and adults feed rapidly, repletion being reached 
in 5 to 10 minutes. Jones has shown the amount of blood required from the 
first instar to adult is only 0.0156 grams for the males and and 0.0209 grams 
for the females. The number of generations per year varies greatly, being 
largely dependent on food supply, temperature, and humidity. During the 
winter season the bedbug is usually inactive but will feed and breed under 
favorable conditions. In warm climates it probably breeds throughout the year,/ 
and the number of generations is probably five or six or more. In colder cli- 
mates there are said to be three or four generations, but no definite number 
can be given as the reproductive and developmental rates are so dependent 
on food supply and warmth. 

1 DISTRIBUTION: This bedbug is cosmopolitan, being found throughout the 
temperate regions of the world and probably in many tropical areas, though 
another species, Cimex hemipterus, is the abundant tropical bedbug;* 1 

idmex hemipterus (Fabr.) is the so-called "tropical bedbug" and is widely 
distributed throughout the tropical and subtropical regions, especially Asia. 
It closely resembles the ordinary bedbug but can be distinguished by the 
lateral margins of the prothorax being rounded and the concave depression 
for the reception of the head being shallower. The habits of the nymphs and 
adults are very similar to those of the common bedbug. The life history is 
almost identical. Dunn found that the time from the hatching of the egg to 
the adult varied from 30 to 40 days. The most interesting feature was that 
each nymphal stage required from two to four meals instead of one. The 
adults live from six to .eight months. Each female is capable of laying from 
about 100 to 439 eggs. 4 

)'' . 

DISPERSAL! Bedbugs are gregarious and remain close to their food supply; 

their dispersal is mainly through man's activities. As bedbugs readily hide 
in clothing and the eggs are laid in all their places .of concealment, their dis- 
tribution is largely dependent on man's carrying them from place to place 
with his household goods or his clothing. A single impregnated female ac- 
cidentally introduced into a household will soon produce a good-sized colony .| 
Furthermore, bedbugs are active migrants and will readily pass from one 
person to anotherlThis has been seen again and again in crowded railway 



ORTHOPTERA AND HEMIPTERA 177 

cars, boats, buses, and other public conveyances. In crowded city houses, apart- 
ments, and tenements they will travel along the water and heating pipes, 
especially if their food supply has been removed. Bedbugs are frequently re- 
ported as very abundant in movie houses. Again bedbugs are capable of with- 
standing long periods of starvation, especially during cold weather, and 
unfrequented houses, as summer hotels, cottages, and similar places may 
remain infested from year to year. As they are known to feed on birds, white 
rats, rabbits, and mice (Patton and Evans record that they fed them on rats, 
cats, dogs, monkeys, rabbits, guinea pigs, and a calf), they can probably 
obtain food to tide them over periods of man's absence. MacGregor mentions 
an interesting case of dispersal. In the East African campaign of World War I 
bedbugs invaded the cork lining of the helmets of the soldiers. As the helmets 
were piled together at night, all soon became infested and the soldiers com- 
plained of bugs attacking their heads. 

if BEDBUGS AND HUMAN WELFARE: Bedbugs affect man in two 
ways: (i) by their bites and bloodsucking propensities; (2) by the possibility 
of their carrying disease-producing organisms or acting as hosts of parasites 
in some phase of the latter's developmental cycle.1 

I BITES: Many persons suffer severely from the bites of bedbugs; many do 
not suffer at all or even know when they are bitten; and others appear immune 
to their attacks. Puri (1924) has shown that the salivary secretion is the cause 
of the irritation and that it contains a rather strong anticoagulin.' Children 
suffer most from bedbug bites. In susceptible persons there is severe irritation, 
hardened wheals may develop at the sites of the bites, and secondary infection 
may follow. In severe cases there may be a marked nervous reaction accom- 
panied by digestive disorders. Stiles records a case diagnosed as neurasthenia 
and treated as such; an examination of the patient's room showed an abun- 
dance of bedbugs; after fumigation a pint of bedbugs was collected and the 
patient promptly recovered. Unfortunately there is very little data on the 
effect of continued attacks of bedbugs. When abundant they cause loss of 
sleep, loss of blood, nervous reactions, digestive disturbances and, in general, 
reduce the vitality so that people, especially children, are more susceptible to 
prevalent diseases. 

| BEDBUGs^Np DISEASE : Owing to the close relation of man and bedbugs it has 
long been thought such bloodthirsty parasites must, in some way, be asso- 
ciated with disease transmission. Though intensive research has been carried 
out along this line, nearly all the results are either negative or inconclusive. 
Bedbugs have been shown experimentally capable of transmitting bubonic 



178 MEDICAL ENTOMOLOGY 

plague (Pasteurdla pestis) even as long as 48 days after an infective meal, yet 
there is no evidence that they play a part in human transmission. Many 
experiments with pathogenic organisms such as those of leprosy, tuber- 
culosis, and typhoid fevers have given negative results. Extensive experiments 
with bedbugs and the causative agents of kala azar (Leishmania donovani) 
and of Oriental sore (Leishmania tropicd) have resulted in failure to transmit 
even under the most favorable conditions. In the case of relapsing fevers 
(Spirochaeta spp.) all experiments have failed, though the bedbugs can be 
infected and the spirochctes remain alive in the gut or the coelomic fluid for 
considerable periods. No transmission took place by the bites of infected 
bedbugs though transmission of the spirochetes was effected by crushing 
infected bedbugs on the scarified skin of experimental animals or by injecting 
the hemolymph of such bedbugs. When relapsing fevers become epidemic 
in the presence of numerous bedbugs, human infection may occur, though 
usually the ordinary human lice (Pedicitlus humanus) are present and are 
effective transmitters. Brumpt has shown that the bedbug (both species) can 
be infected with Trypanosoma crnzi (causative agent of Chagas* disease), and 
he caused animal infection through the feccs. This work was confirmed by 
Mayer and da Rocha-Lima. No infection occurred by the bites of infected 
bedbugs. Francis has shown that Cimex lectularius can transmit tularemia 
(Bacterium tularense) from mouse to mouse by its bites up to 71 days after 
the bugs had their infective meal. Mice also contracted the disease by eating 
bedbugs that had been infected 65 to 100 days previously. He also showed 
that the feces of infected bugs contained the virulent organisms of tularemia at 
all times to at least 250 days after the date of infection. 

OTHER SPECIES OF CIMICIDAE: Leptocimex boueti (Brumpt) oc- 
curs in French West Africa and is quite widely distributed. According to 
Joyeux (1913) its life history is very similar to that of the ordinary bedbug 
as it readily feeds on man. It may be recognized by its very long legs and much 
narrower body. Cimex pilosellus Horvath and C. pipistrelli (Jenyns) are 
common parasites of bats, the former in America and the latter in Europe. 
These bugs will invade sleeping rooms and attack man when their normal 
hosts are driven away. In the genus Oeciacus the body is clothed with long 
hairs and the last two segments of the antennae are but slightly thinner than 
the preceding ones, and about equal in length; the front margin of the pro- 
notum is shallowly concave. O. vicarius Horvath, the common bedbug of 
swallows in North America, will invade dwellings when their nests are located 
on houses and infested with this bug; O. hirundinis (Jenyns), the barn-swallow 
bug of Europe, will also attack man and its bite is said to be severe. Cimexopsis 



ORTHOPTERA AND HEMIPTERA 179 

nyctalis List has been recorded in Nebraska as attacking man, though its 
normal hosts are thought to be chimney swifts (Chaetura). Hacmatosiphon 
inodora (Duges) is a large bug that normally infests poultry houses in the 
southwestern United States and Mexico; it has also been reported from Flor- 
ida. It sometimes invades houses and frequently becomes a serious pest. Its 
bite is severe. 

CONTROL OF BEDBUGS During World War II an almost perfect 
method for the control of bedbugs was developed. By the proper use of DDT 
bedbugs can not only be controlled but eliminated from all their breeding 
places. Depending on the place to be treated either a 5 per cent DDT solution 
or emulsion can be used. Where it is not feasible to use a spray, a 10 per cent 
dust may be employed, though it does not give such satisfactory results. 

The 5 per cent DDT spray (solution or emulsion) can be applied by a small 
hand sprayer, by a knapsack type sprayer, or by power equipment. In treat- 
ing an infested room or building it is essential first to clean the place. Then 
spray all beds, especially the mattresses, bedsprings, joints, and corners, thor- 
oughly with a wet spray, not a mist. Then treat all cracks, crevices, especially 
behind baseboards, picture frames, loose wallpaper, and, if the place is badly 
infested, every part of the room. The spray will kill all bedbugs it covers, but 
many may not be reached. However, the residual DDT on the walls, bedding, 
and beds will kill all bugs that come in contact with it. Experiments have 
shown that the residual action is very lasting, at least a year. If spraying cannot 
be used, dust with a 10 per cent DDT powder on mattresses, bedding, cracks, 
crevices, and similar places. The bedbugs will be killed by walking over the 
powder. By the proper and timely application of any of these methods bedbugs 
can be eliminated. 

Sulphur fumigation is also effective but it involves much more labor and 
trouble. When sulphur is used, the rooms must be prepared by the closure 
of all cracks, crevices (as around doors and windows), keyholes, and other 
openings by pasting over them strips of heavy brown paper. (Thin flour paste 
or merely water will serve for temporary attachment; soak the brown paper 
in water till saturated; then apply it and it will stick for several hours.) All 
metallic objects and fabrics that might be bleached by the sulphur fumes 
should be removed. Metals that cannot be removed should be coated with 
vaseline. Large openings such as fireplaces must be closed. The sulphur is 
used at the rate of four pounds to 1000 cubic feet of space. The sulphur should 
be burned in a large iron pan or pot placed on bricks in a galvanized tub 
containing some water. This will take care of any spilling and prevent injury 
to the floors. Pour a small amount of denatured alcohol on the sulphur (aboul 



i8o MEDICAL ENTOMOLOGY 

a cup to four pounds of the sulphur) and ignite the alcohol. Several such out- 
fits may be placed in different parts of the place to be fumigated. All should 
be started at about the same time. Then the building should remain closed 
for several hours, at least four or five. Sulphur candles may also be used, but 
great care should be employed to avoid danger from fire and enough candles 
must be burned. 

Fumigation with hydrocyanic acid gas is a very effective control method 
but should be undertaken only by responsible personnel. The building to be 
fumigated should be prepared as for sulphur fumigation. The necessary 
ingredients are sodium or potassium cyanide (these can be obtained in the 
form of small eggs, each weighing about one ounce), a commercial grade of 
sulphuric acid, and water. It requires at least one ounce of the cyanide for 
each 100 cubic feet of space. The mixture is prepared as follows: 

Sodium cyanide (95 to 97 per cent purity) i ounce 

Sulphuric acid i ]X> fluid ounces 

Water 2 fluid ounces 

In the fumigation of a building, the cubic contents must be calculated, the 
distribution of the fumigation pots should be designated, and the amount 
of ingredients for each pot determined. The equipment should consist of five- 
to eight-gallon earthenware crocks. The crocks should be placed on thick folds 
of paper to avoid injury from splashing. In each of the crocks place the deter- 
mined amount of water and then add the sulphuric acid, pouring slowly (never 
the reverse process). Beside each crock place the determined amount of sodium 
cyanide, preferably in a thin paper bag. When all is in readiness start at the 
top floor and drop the cyanide into the jars, passing to the floors below as 
rapidly as possible. The gas is very light and is given off very rapidly. The 
house or building should be kept closed for at least 12 hours and then aired 
by opening the windows and doors from the outside. Keep open for another 
6 to 12 hours before entering unless gas masks are used. Fumigation with 
hydrocyanic acid gas should be undertaken only by trained persons and gas 
masks should be used. 

Another fumigation method is the use of thin discs impregnated with 
liquid hydrocyanic acid. These discs (Zyklon discoids) are conveniently 
packed, and full directions for their use are furnished. Gas masks should be 
employed when using such discs. Pyrethrum aerosol bombs are also effective 
and they are nonpoisonous. 

In most of our states and particularly our large cities the Boards of Health 
have strict regulations governing the use of poisonous gases. Such rules and 
regulations should be carefully followed before attempting any fumigation. 



ORTHOPTERA AND HEMIPTERA 181 

THE FAMILY REDUVIIDAE-THE ASSASSIN BUGS 

The Reduviiclae is a large family of predaceous bugs that suck the blood 
and lymph of their prey. At least 400(3 species are known. They feed mainly 
on other insects and on each other. However, certain groups attack man and 
some of these are important vectors of human and other animal diseases. Their 
bites are frequently severe and often difficult to heal. The assassin bugs are 
rather elongate, active, large insects. The beak is stout, three-segmented, and 
capable of inflicting a painful wound. The head is freely movable and more or 
less elongate, and the eyes are conspicuous. The ocelli arc prominent when 
present and the antenna is four-segmented. The family is divided into a large 
number of subfamilies and numerous genera. Although nineteen subfamilies 
are listed by Usinger (1943), only about three contain genera that are at present 
known to plague man, and some of these are not of great importance. The 
following brief summary may aid in recognizing these subfamilies: 

KEY TO THE SUBFAMILIES HAVING SPECIES THAT 
ATTACK MAN 2 

1. Beak divided into 3 segments and fits into a cross-striated groove; stout, 

short, not reaching the middle coxae; ocelli, when present, placed dis- 
tinctly behind the eyes or behind a transverse depression 

Family Reduviidae 2 

2. Wing membrane with one or more closed cells; front coxae not greatly 

elongated, usually less than twice as long as broad and not extending 
beyond apex of head 3 

3. Pronotum constricted behind the middle; ocelli present. Subfamily Pira- 

tinae (Genera Melanolestes, Rasahus, and others; Fig. 74) 
Pronotum constricted at or near the middle 4 

4. Ocelli present and located behind the compound eyes; second antennal 

segment not subdivided 5 

5. Head rarely constricted behind the eyes. Elongate; ocelli located on 

oblique elevations or tubercles at posterolatcral angles of the long, cylin- 
drical head; dorsal abdominal glands absent .... Subfamily Triatomi- 
nae (Here belong Psamntolestes, Rhodnius, Eratyrus, Panstrongylus, 
Triatoma, and others) 
Head transversely constructed behind the eyes; eyes not stalked; antennae 



2 Keys to the genera and species of Triatominae will be found by consulting the ref- 
erences at the end of the chapter. 



1 82 MEDICAL ENTOMOLOGY 

not inserted on long, oblique tubercles; dorsal scent glands present 

(Reduvius, Spiniger, and others) Subfamily Reduviinae 

The Subfamily Triatominae 

The known members of this subfamily as at present restricted feed exclu- 
sively by sucking the blood of vertebrates. Though widely distributed, the 
great majority of the species are predominantly American. A few species 
occur in the Oriental and African regions, and Triatoma rubrojasciata (De 
Geer) is tropicopolitan. Usinger (1944) recognizes 9 genera and 40 species 
and subspecies from North and Central America, Mexico, Panama, and the 
West Indies. Costa Lima (1940) recognizes 9 genera and 44 species from Brazil 
and neighboring countries. Neiva and Lent (1941) list 14 genera and 89 species 
from the world. The study of this subfamily is of great importance in the 
Americas since the discovery by Chagas (1909) that a certain species, Pan- 
strongylus megistus, is the intermediate host of a disease (Chagas' disease) 
caused by Trypanosoma cnizi. Since then a large number of species have been 
shown to harbor the trypanosome and many of them to transmit the disease. 
Only a few of the species can be discussed here with a list of the more im- 
portant vectors of the disease and their known distribution. 

Panstrongylus megistus (Burm.) was the first species shown by Chagas to 
be the natural vector of the disease that bears his name. The species is widely 
distributed in Brazil, British Guiana, and Paraguay. This bug is primarily 
domestic and hides in cracks, crevices, or any available cover during the day. 
At night it comes out to feed and its bite is not recorded as severe. The adults 
measure from 30 to 32 mm. in length. They are black, with regularly arranged 
red markings on the prothorax, wings, and abdomen (Fig. 72). They are 
strong fliers and readily migrate from house to house. The female lays her 
eggs in batches (8 to 12 in a batch) in the cracks, crevices, and holes in the 
floors and walls. Each female lays from 160 to 220 or more eggs. The eggs 
hatch in from 8 to 30 days. The nymphs feed on humans at night. There are 
five nymphal stages and each nymphal stage requires a number of blood meals. 
The entire life cycle from egg to adult varies from 260 to 300 days. 

Triatoma rubrojasciata (De Geer) is widely distributed in the Oriental re- 
gions, parts of the Ethiopian region, neotropical region, the West Indies, Cen- 
tral America, and Florida in the United States. It is quite domestic in its habits 
and its bite is rather severe. Its life history is very similar to that of the preceding 
species. Patton and Cragg found, under experimental conditions, that the 
life cycle from egg to adult required from four and one-half to five months. 

Triatoma sanguisuga (Le Conte) is the big bedbug or conenose (Fig. 73) 



ORTHOPTERA AND HEMIPTRRA 183 

of the south and western United States, extending north to Pennsylvania and 
west to Kansas, Texas, and Mexico; it is reported from Panama. It infests 
poultry houses and the adults invade human habitations. The adult is 1 8 to 
20 mm. in length, flattened, and dark brown in color with pinkish or reddish- 




Fig. 75. The bloodsucking conenose, Triatoma sanguisuga. (a) and 
Nymphal stages. (<:) Adult, (d) Lateral view of adult to show long beak. 
(After Marlatt.) 

orange areas on the abdomen, on the tips and bases of the hemelytra, and along 
the anterior and lateral margins of the pronotum. Recently several subspecies 
have been described but on rather minor characters. 

The life histories of a number of species have been fully elucidated in recent 
years: Euratyrus cuspidatus Stal and Panstrongylus geniculatus (Latr.) by 
Hase (1932); Rhodnius prolixus Stal by Buxton (1930); Triatoma dimidiata 
'(Latr.) by Campas (1923); and Paratnatoma hirsuta Barber (two-year life 



184 MEDICAL ENTOMOLOGY 

cycle), T. rubida uhleri (Neiva), one-year life-cycle, T. lecticularius occulata 
(Neiva), one-year life cycle, T. gerstaecferi (Stal), one-year life cycle, T. 
longipes Barber (two-year life cycle), and T. protracta (Uhler), one-year life 
cycle, all by Usinger (1944). 

. TRIATOMINAE AND THEIR RELATION TO DISEASE: BITES: 
The bites by a number of species are known to be severe but others cause little 
if any reaction. Numerous records of severe reaction from their bites are 
known. However, Wood (1942) tested eight common species (Triatoma pro- 
tracta woodi, T. longipes, T. gerstaecl^cri, T. lecticularius, T. sanguisuga, T. 
rubida, and Paratriatoma hirsuta) without any ill effects except a tickling 
sensation. 

DISEASE: The only disease so far definitely associated with these bugs is 
Chagas' disease caused by Trypanosoma cruzi. In 1909 Chagas announced suc- 
cessful transmission of an unknown disease in Brazil by Panstrongylus megis- 
tus caused by a trypanosome and described by him as Trypanosoma cruzi. 
This disease was later differentiated as a specific entity and bears the name of 
Chagas' disease. The disease is widespread and occurs from Argentina through 
much of South America, Panama, Central America, and Mexico. The disease 
is characterized by fever, swelling of the eyelids and face, enlargement of 
various lymphatic glands, and destruction of the cardiac muscles of the heart, 
the cells of the spleen and the brain, and endothelial tissue cells generally 
throughout the body. The disease appears in two forms, acute and chronic. 
In the acute stage death may occur in two to four weeks, In the chronic state, 
mostly in adults, the disease runs a varied course. At present there seems to be 
no adequate treatment. 

TRANSMISSION: The various species (see Table 6) obtain the trypanosomes 
from the infected reservoir hosts when taking blood. In the bug the trypano- 
somes develop only in the lumen of the intestinal tract. First they develop 
into crithidial forms in the stomach; migrating posteriorly they transform to 
smaller forms and give rise to the metacylic (infective) trypanosomes. These 
are discharged in the feces, and infection in man takes place when the feces 
are deposited at the time the bug is feeding or soon after. They gain access to 
the body through abrasions of the skin (by scratching or otherwise) or the 
mucous membranes of the mouth, conjunctiva of the eyes, or other moist mem- 
branes. Other animals become infected in a similar manner or by eating in- 
fected bugs. The life cycle in the bug requires 6 to 15 days, and once infected 
the bug remains capable of transmitting the disease for a long time, at least 
one or two years according to some authorities. In man the incubation period 



ORTHOPTERA AND HEMIPTERA 185 

is 10 to 12 days and the trypanosomes may be found in the blood during this 
period. Later they disappear from the blood and are found in the Leishmania 
form in the cardiac muscles and in cells of the spleen, liver, brain, and most of 
the tissues. From time to time the trypanosome form appears in the circulating 
blood and man may serve as a reservoir for the bugs. As this disease is wide- 
spread, it has become of great importance. Though the trypanosome is present 
in many triatome bugs in the United States, no human case has been discovered. 
However, these infected bugs do bite humans and Packchanian (1943) has 
produced a typical infection in a human being with trypanosomes from Texas 
(crushed infected Triatoma heidemanni). He also infected monkeys (Macacus 
rhesus} and deer mice (two species). He recovered the trypanosomes from all 
cases and cultured them. Despite this experimental evidence no human cases 
of Chagas' disease have been isolated in the United States. Undoubtedly some 
must occur, but they have not been diagnosed as such. 

Table 6. Tritomc bugs found naturally infected and their distribution. 



Species 

Triatoma barberi Usinger Mexico 

Triatoma brasilicnsis Neiva Brazil 

Triatoma chagasi Brumpt and Gomes Brazil 

Triatoma dclpontei Romana and Abalos Argentina 



Distribution 



18. 
19. 



Triatoma dimidiata (Latr.) 

Triatoma gcrstaecl^cri (Stal) 
Triatoma hcgncri Maz/.otti 
Triatoma injestans (Klug.) 

Triatoma JecticuJarius (Stal) 

(hcidcnmanni Neiva) 
Triatoma longipcs Barber 
Triatoma phyllosoma (Burm.) 

var. longipennis (Usinger) 
var. pallidipennis (Stal) 
var. picturata (Usinger) 
Triatoma platcnsis Neiva 
Triatoma protracta (Uhler) 

var. woodi (Usinger) 
Triatoma rubida uhlcri (Neiva) 
Triatoma rubrojasciata (de Geer) 
Triatoma rubrovaria (Blanchard) 
Triatoma sangnisuga (Lee.) 

var. ambigua (Neiva) 
var. indictiva (Neiva) 

Triatoma spinolai Porter 
Triatoma vitticcps (Stal) 



Mexico, Central America, Panama, 

Venezuela, Peru 

Mexico, U.S.A. 

Mexico 

Brazil south to Argentina, 

Chile, Peru 

U.S.A. (Texas) 

U.S.A. (Arizona) 

Mexico 

Mexico 

Mexico 

Mexico 

Argentina 

California, New Mexico, Arizona, Texas 

Texas 

U.S.A. (California and Arizona) 

Tropical regions of world 

Argentina, Chile, Uruguay 

U.S.A., Mexico, Panama 

U.S.A. 

U.S.A. (Arizona, New Mexico, 

Texas) and Mexico 

Chile 

Brazil 



i86 



MEDICAL ENTOMOLOGY 



20. Dipetalogaster maxim us Usinger 

21. Eutriatoma maculata (Erichson) 

22. L-Mtriatoma nigromaculata (Stal) 

23. Eutriatoma oswaldol (Neiva and Pinto) 

24. Eutriatoma patagonica del Pontc 

25. Eratyrus cuspidatus Stal 

26. Ncotriatoma circummaculata (Stal) 

27. Panstrongylus geniculatus (Latr.) 

28. Panstrongylus megistus (Burm.) 

29. Panstrongylus rujotuberculatus 

(Champion) 

30. Rhodnius brumpti Pinto 

31. Rhodnius domcsticus Neiva and Pinto 

32. Rhodnius pallesccns Stal 

33. Rhodnius prolixus Stal 

34. Cavernicola pilosa Barber 

35. Psammolestes arthuri (Pinto) 



Mexico (cape region of 

Baja California) 

Brazil north to Venezuela 

Venezuela 

Argentina 

Argentina 

Panama, Colombia, 

Venezuela 

Argentina, Uruguay 

Argentina north to 

Venezuela, Panama 

Paraguay, Brazil north to 

Venezuela 

Panama, Ecuador, Venezuela 

Brazil 

Brazil 

Panama 

Brazil north to Colombia, 

San Salvador, Mexico 

Brazil 

Venezuela 



In addition to the list of species given above, a long series of other Hemip- 
tera are recorded as capable of acting as vectors of Chagas' disease. Some of 
these are dm ex lectularhis, C. hemipterus, C. stadleri, Leptocimex boutei, 
Oeciactts hirundinis, and Haematosiphon inodora. The following ticks are 
also indicated: Ornithodoros moubata, O. talaje, O. venezuelensis (rudis), 
O. conlceps, O. lahorensis, O. nicollei, Amblyomma cajennense, and Rhipi- 
cephalus sanguineus. 

The vectors of Chagas' disease do not, in most cases, normally live in human 
dwellings but feed on a great variety of wild animals. Many of these animals 
serve as a reservoir for the trypanosome since none of the bugs are known to 
transmit Trypanosoma cruzi to their offspring. Furthermore many of the 
triatomes feed on more or less specific hosts, and a large number of these hosts 
have been examined and found to harbor Trypanosoma cruzi either in their 
blood or as Leishmania forms within tissue cells. From these hosts the triatome 
bugs obtain their infection and may transmit it to man. Some of the known 
reservoirs are: armadillos (8 or more species) in Brazil, Panama, Mexico, and 
Texas (mostly Dasypus novemcinctus and its varieties) ; bats in Panama and 
California (Artibeus jamaicensis, Carollia perspicullata azteca, Desmodus 
rotundas murinus, Glossophaga soricina leachi, Phyllostomus hastatus pana- 
mensis, and Uroderma bilobatum in Panama; Antrozous pallidus pact feus in 
California) ; cats and dogs in Brazil, Panama, Guatemala, and Mexico; house 
mice in the United States; opossums in Honduras, Panama, and the United 



ORTHOPTERA AND HEMIPTERA 187 

States; wood rats (Neotoma species) in Mexico, California, Texas, and other 
states. In addition, many animals are easily infected experimentally as mice 
(10 or more species), monkeys, rats, rabbits, dogs, and many others. 

OTHER REDUVIID BUGS THAT SUCK BLOOD; A large number of 
reduviid bugs have been recorded as occasionally attacking man, and their 
bites frequently prove very annoying. The following are the most important 
species : 

Rhodnius prolixus Stal is a domestic bug prevalent in parts of South America 
and San Salvador. It readily bites man and is the natural vector of Chagas' 
disease in Venezuela. 

Reduvius personatus Linn. (Fig. 74) has received a rather bad reputation 
for attacking people and has been called the "kissing bug." This bug is com- 
monly found in houses in many parts of the world. The nymphs are covered 
with a sticky substance to which dirt, dust, and floss adhere. They are said to 
feed on bedbugs, flies, etc., and the nymphs are frequently called the "masked 
bedbug hunters." The adult is almost coal black, very active, and attracted to 
lights. It measures about 20 mm. in length. When handled roughly as in 
attempts to remove them when they alight on the face or hands, they bite 
readily and fiercely. Herms quotes reporting physicians as stating, "In a few 
minutes after the bite the patient develops nausea, palpitation of the heart, 
rapid breathing, rapid pulse, followed by profuse urticaria all over the body." 
Like all other insect bites, the effects depend largely on the susceptibility of 
the individual. 

Rasahus biguttatus Say (Fig. 74) and Rasahus thoracicus Stal are known 
as the "Corsairs." The former occurs in the southern states and the West Indies, 
the latter in the western part of the United States and probably Mexico. The 
bites of these bugs are quite severe and have been confused with spider bites. 

Arilus cristatus Linn, the "wheel bug," so-called because of the cogwheellike 
crest on the prothorax, is normally predaceous on other insects. Hall (1924) 
records a young girl being bitten twice by this bug on her little finger. This 
was followed by severe pain, and growths resembling papillomas developed 
at the sites of the bites. The growths persisted for months, and the finger 
remained warmer than the others for over a year. The bug is distributed in 
North America from New Jersey southward. 

Mdanolestes picipes H. S. (Fig. 74) is an almost coal-black bug found com- 
monly throughout North America. There are well-authenticated records of 
its biting man. It is found under stones, logs, moss, etc., and will bite if handled 
roughly. It is also reported as flying into houses, being attracted by the lights, 
and biting. Its bite is said to be severe. 



1 88 MEDICAL ENTOMOLOGY 

Mdanolestes abdominalis H.S. is also recorded as biting man. It is widely 
distributed in North America and has about the same habits as M. picipes. 

Many other species of Hemiptera have been reported as occasionally attack- 
ing man. The reports of the effects of their bites vary so widely that no general 
statement regarding them can be made. It should be borne in mind that the 
bite of a bug is always more or less complicated not only by the susceptibility 
of the individual to protein substances (fluid from the salivary or poison 




Fig. 74. Three reduviids that commonly bite man. (A) Reduvius personatus (the so- 
called "kissing bug"). (B) Me/anolestes picipes. (C) Rasahns biguttatus. 

glands of the bug) but also to any contamination present on the proboscis. 
The latter feature seems often to be overlooked when the ill effects of a bite 
are described. The following incomplete list will give some idea of the numer- 
ous observations recording the bloodsucking habits of bugs : 

Nabidae 
Nabis capsijormis Germar. Cosmopolitan in the tropics. 

Anthocoridae 

Anthocoris musculus Say. Biting hop pickers. 
Anthocoris sylvestris Linn. Europe. 
Anthocoris \ingi Brumpt. Sudan. 
Anthocoris insidiosus Say. North America. Several records of this bug biting 

man. 

Cardiastethus elegans Uhl. Panama. From bats. 
Lyctocoris campestris Fabr. Europe and North America. 

Pyrochorridae 

Clcrada apicicornis Sign. Widely distributed in the tropics. 
Dysdcrcus superstitiosus Fabr. Africa. 



ORTHOPTERA AND HEMIPTERA 

Lygaeidae 

Leptodemus minutus Jakovleff . Mediterranean region. 
Geocoris hconi Puton and G. scutdlaris Puton. North Africa. 

Miridae (Capsidae) 

Plagionathus obscurus Uhler. North America. 
Lygus pratensis Linn. North America, Europe, Asia. 

Notonectidae 

These are aquatic insects, the so- 
called "back swimmers." Practically 
all the larger species will bite if handled 
roughly. The bite is quite severe. 

Belostomatidae 

These are the giant water bugs (Fig. 
75) and include the largest of our 
Hcmiptera; some species exceed three 
inches in length. They are found com- 
monly in stagnant, water. The adults 
are strongly attracted to lights and 
hence have been called "electric light 
bugs." Their bites, especially those of 
the larger species, are quite severe. The 
author has recorded the death of a 
good-sized woodpecker, killed by 
Lethocerus americanus; the bug had 
inserted its beak deep into the back 
part of the skull. 




Fig. 75. A giant water 
bug, Ecnacus griseus. 



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190 MEDICAL ENTOMOLOGY 

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. Life-history of the tropical bedbug (Cimex rotundatus} in Panama. Ibid., 

4 : 77~ 8 3> J 9 2 4- 
Fracker, S. B. A systematic outline of the Reduviidae of North America. Iowa 

Acad. Sci., 19: 217-252, 1914. 
Francis, Edward. The transmission of tularaemia by the bedbug, Cimex lee- 

tularius. U.S. Pub. Hlth. Serv., Hyg. Lab., Bull. 130: 24-37, 1922. 
Girault, A. A. Preliminary studies on the biology of the bedbug, Cimex lee- 

tularius Linn. Jl. Econ. Biology, 5: 88-91, 1910; 7: 163-188, 1912. 
Hall, M. C. Lesions due to the bite of the wheelbug, Arilus cristatus (Hemiptera, 

Reduviidae). Arch. Internal Med., 33: 513-515, 1924. 



I 9 2 MEDICAL ENTOMOLOGY 

Horvath, G. Revision of the American Cimicidae. Ann. Hist. Nat. Hung. 

(Budapest), 10: 257-262, 1912. 
Howard, L. O. The insects to which the name "kissing bugs" became applied 

during the summer of 1899. U.S. Dept. Agr., Div. Ent. Bull. 22: 24-30, 1900. 
Hussey, R. F. A bibliographical notice on the reduviid genus Triatoma. Psyche, 

29: 109-123, 1922. 
Jones, R. M. Some effects of temperature and humidity as factors in the biology 

of the bedbug (Cimex lectularius Linn.). Ann. Ent. Soc. Amer., 23: 105-119, 

1930. 

Joyeux, Charles. Biologic de Clmex boueti. Arch. Parasit., 16: 140-146, 1913. 
Larrousse, F. Etude biologique et systematique du genre Rhodnius Stal. 

(Hemiptera, Reduviidae). Ann. Parasit. Hum. Comp., 5, 63-89, 1927. 
McCiure, H. E. The bite of Melanolestes picipes. Ent. News, 46: 138-139, 1935. 
Marlatt, C. L. The bedbug and cone-nose. U.S. Dept. Agr., Div. Ent. Bull. 4: 

32-42, 1896. 
Mazzotti, L. Experimental infection of Haematosiphon inodorus (Duges) with 

Trypanosoma cruzi Chagas. Bull. Brokl. Ent. Soc., 36: 67-68, 1941. 
Mellanby, K. A comparison of the physiology of the two species of bedbugs which 

attack man. Parisitology, 27: 111-122, 1935. 
. Fertilization and egg production in the bedbug, Cimex lectularius L. Ibid., 

31: I93-I99.I939- 
. The physiology and activity of the bedbug (Cimex lectularius) in a natural 

infestation. Ibid., pp. 200-211, 1939. 
Monteiro, }. L. Sobre a transmissao do virus da febre amarella pelas fezes de 

presevejos infectados. Brasil-Meclico, 43: 1037-1040, 1929. 
Myers, L. E. The American swallow bug, Oeciacus vicarius Horvath. Parasitol- 

ogy, 20: 159-172, 1928. 
Myers, }. G. Facultative blood-sucking in phytophagous Hemiptera. Ibid., 21: 

472-480, 1929. 
Neiva, A. Informaqois sobrc biolojia do Conor hinus megistus Burm. Mem. do 

Instit. Oswaldo Cruz, 2: 206-212, 1910. 

, and Lent, H. Sinopse dos triatomideos. Rev. Ent., 12: 61-92, 1941. 

Pinto, C. Ensaio monographico dos reduvideos hematophagos o "barbeiros." 

Rio de Janeiro, 1925. 
Ponte, E. del. Catalogo descriptico de los generos Triatoma Lap., Rhodnius Stal., 

y Eratyrus Stal. Rev. Inst. Bact. (Buenos Aires), 5: 855-937, I 93- 
Puri, I. M. Studies on the anatomy of Cimex lectularius. i, n. Parasitology, 

16: 84-97, 269-278, 1924. 
Readio, P. A. Studies on the biology of the Reduviidae of America, north of 

Mexico. Univ. Kansas Sci. Bull., 17: 5-291, 1927. 
Richardson, H. H. Studies of methyl bromide, chloropicrin, certain nitriles and 

other fumigants against the bedbug. Jl. Econ. Ent., 36: 420-426, 1943. 



ORTHOPTERA AND HEMIPTERA 193 

Rivnay, E. Studies in tropisms of the bedbug, Cimex Icctularius L. Parasitology, 
24: 121-136, 1932. 

Rosenholz, H. P. Die Rolle der Wanzen in der Epidemiologie des Rikkfallfiebers. 
Central. Bakt. I Abt., Orig., 102: 179-213, 1927. 

. Weitere Untersuchungen iiber die Rolle der Wanzen in der Epidemiologie 

des Ruckfallriebers. Ibid., 103: 348-353, 1927. 

Roubaud, E. Adaptation spontanee de la punaise des lit (Cimex lectularius) en 
milieu obscuricole, aux rongeurs domestiques. Bull. Soc. Path. Exot., 21: 224- 
226, 1928. 

Rozeboom, L. E. Triatoma dimidiatu Latr., found naturally infected with Try- 
panosoma cruzi Chagas in Panama. Amer. Jl. Trop. Med., 16: 481-484, 1936. 

Sherrard, C. Five fuinigants for disinfestation of bedding and clothing; a com- 
parative study of insecticide properties. U.S. Pub. Hlth. Repts., 57: 753-759, 
1942. 

Torre-Bueno, J. L. Biting bugs. Bull. Brokl. Ent. Soc., 26: 176, 1931. 

Usinger, W. E. The Triatominae of North and Central America and the West 
Indies and their public health significance. U.S. Pub. Hlth. Serv., Bull. 288, 
1944. 

Wood, F. D., and Wood, S. F. On the distribution of Trypanosoma in the south- 
western United States. Amer. Jl. Trop. Med., 18: 207-212, 1938. 

Yorke, W. Chagas' disease: a critical review. Trop. Dis. Bull., 34: 275-300, 



CHAPTER VII 



The Order Anoplura: 
The Biting and Sucking Lice 



THE order Anoplura contains the sucking lice and the biting lice of 
mammals and birds. It has been generally held, and still is by some, that 
these two groups constitute distinct orders, the Siphunctilata (the sucking 
lice) and the Mallophaga (the biting lice). However, all the recent morphologi- 
cal and biological evidence seems to indicate that the two groups arc so closely 
related that they constitute but suborders of the Anoplura. 

CHARACTERISTICS 

v The Anoplura are wingless insects that live permanently as ectoparasites on 
mammals and birds, upon whose hairs (and clothes in man) or feathers they 
cement their eggs, The antennae are short, three- to five-jointed; the eyes are 
reduced or absent; the ocelli are lacking. The mouth parts arc strikingly modi- 
fied cither for piercing and sucking blood (Siphunctilata) or for feeding on 
the scales, feathers, scurf, and wastes of the skin (Mallophaga). The thoracic 
segments are more or less fused; the legs are rather short and fitted for cling- 
ing; the tarsi are one- or two-jointed and terminate in one or two claws. The 
metamorphosis is incomplete. 

The order contains two suborders, the Siphunculata and the Mallophaga. 
The Mallophaga are not known to transmit disease. 

THE SUBORDER SIPHUNCULATA 

The Siphunculata or sucking lice are all permanent ectoparasites of mam- 
mals. The mouth parts (Fig. 79) are highly modified and, when at rest, are 
retracted within a divertictilum that opens into the floor of the pharynx at 
its anterior end. The thoracic segments are fused (except in the genus Haema- 



THE ORDER ANOPLURA 195 

tomyzus) ; the tarsi are one-segmented and terminate in a single claw which 
is fitted for grasping and clinging to hairs. 

The Siphunculata is a very small group (only somewhat over 200 species 
have been described from the world), consisting exclusively of bloodsucking 
ectoparasites of mammals. At the present time four families are recognized. 1 
Of these families only one, the Pediculidae, contains species that affect man 
himself. The following simple key will aid in -distinguishing the families: 

1. Head prolonged as a narrow tube; tibiae lacking a thumblike process 

opposing the claw; prothorax distinct. (Pflly one genus and one species, 

Haematomyzuselephantis,on elephants) Haematomyzidae 

Head not prolonged as a tube; tibiae with a thumblike process (Fig. 78) 
opposing the claw; prothorax not distinct 2 

2. Body distinctly flattened; sparsely clothed with setae or spines that are 

arranged in more or less definite rows; parasites on land mammals .... 3 
Body rather thick and stout; clothed with stout, heavy spines, and, in 

some cases, scales. Parasites exclusively on marine mammals 

Echinophtheriidae 

3. Eyes present, pigmented; head not retracted into the thorax. Parasites of 

man, monkeys, and apes Pediculidae 

Eyes absent or vestigial; head rather deeply retracted into the thorax. 
(This family contains more than half of the described species of lice) 
Haematopinidae 

THE FAMILY PEDICULIDAE 

The family Pediculidae 2 has been divided into two subfamilies, the Pedi- 
culinae and the Pedicininae. The former are characterized by a five-jointed 
antenna and occur on man, monkeys, and apes; the latter have the antenna 
three-jointed (indistinctly five-jointed) and are found on monkey**. The 
entire family contains some four genera and less than twenty species and 
varieties, many of them scarcely deserving the designation of more than races. 
The forms known from man are Pediculus humanus Linn., of which there 
are two varieties or races P. humanus var. capitis de Geer (the head louse) 
and P. humanus var. corporis de Geer (the body louse) and Phthirus pubis 
(Linn.) (the groin, crab, or pubic louse) . 

x Ewing (1929) recognizes six families, but the creation of two new families for a 
few rather aberrant species does not seem warranted. 

2 Ewing (1929) has created a new family for the pubic louse (Phthirus pubis Leach); 
has accepted most of Fahrenholz's genera and species; and, at the same time, has de- 
scribed a number of new varieties. 



196 MEDICAL ENTOMOLOGY 

THE HEAD LOUSE: Pediculus humanus var. capitis de Geer (Fig. 76) 
is the head louse of man. This variety or race is found principally on the 
head, living amongst the hair, on which it cements its eggs. It is found most 
commonly at the back of the head and above the ears, though the entire scalp 
may be infested. It also may occur on the eyebrows and the hairy parts of the 
body, and I have seen the eyelashes of an infant with a louse deeply embedded 
at the base of nearly every hair. On the average it is smaller than the body 
louse. The female measures about 2.4 to 3.3 mm. in length and the male aver- 




Fig. 76. The human louse, Pediculus humanus. Male at left, female at right. (After 
Nuttall.) 

ages about 2 mm. It is grayish in color, with the margins of the abdomen 
somewhat darker or almost black. In the male (Figs. 76,80) the abdomen is 
rounded at the posterior end and the male genital organ, the aedeagus, is easily 
visible and usually extruded; in the female the terminal portion of the abdomen 
is deeply cleft (Fig. 76). 

THE HEAD: In this louse the head is rounded in front and rather bluntly 
pointed; it is sharply constricted at the insertion of the antennae, then bulges 
sharply and gradually narrows to the neck. The neck is short but permits of 
considerable movement. The antennae are short and five-jointed. The eyes 
are prominent, heavily pigmented, but without facets. The thorax appears as 



THE ORDER ANOPLURA 197 

a consolidated box widening posteriorly. To it are attached the legs, and there 
is a single pair of spiracles on the mesothoracic segment. The abdomen con- 
sists of nine segments, seven of which can be easily counted. The margins are 
festooned and chitinized to form darkly pigmented plates on which spiracles 
are located. There are six pairs of abdominal spiracles. 

THE LEGS: This louse has stout legs, well fitted for clasping and holding. 
The coxa, trochanter, femur, and tibia are well developed (Fig. 77). The 



finale lav 




Fig. 77 (left). Pediculus humanus. Male with parts labeled. (After Nuttall, Para- 
sitohgy.) 

Fig. 78 (right). Pediculus humanus. Terminal portion of first left leg of male. C, claw; 
L, lamella; S, sensory spines; Sp, chitinous spine of thumb; T, tibial thumb; Tar, tarsus; 
Tb, tibia. (After Nuttall.) 

tarsus consists of a single segment and bears a stout, recurved claw. The claw 
can be firmly apposed to a peculiar extension of the inner distal end of the 
tibia, the so-called "tibial thumb" (Fig. 78). The tibial thumb bears a promi- 
nent spine, and by apposing the claw against it the louse can attach very firmly 
to hairs, In the male the, tibial thumb is better developed than in the female. 

MOUTH PARTS i The mouth parts (Fig. 79) of lice are extremely complicated. 
They have been fully elucidated by Sikora (1916), Harrison (1916), Peacock 
(1918), and Florence (1921), but these workers are not entirely in agreement. 
At the front of the head is found a tubelike projection, the haustellum. It is ' 



198 



MEDICAL ENTOMOLOGY 

Ph B 



Fc 




Fig. 79. The mouth parts of a louse (Pediculus humanus). (a) Longitudinal section of 
the head to show the relation of the various parts. (&) The stylets removed and shown 
more in detail, (c) The tip of the ventral stabber or stylet (greatly enlarged), (d) Re- 
construction of the mouth parts near the anterior end to show passage of food canal be- 
tween the dorsal slabbers or stylets. B, brain; D, denticles or teeth; DSt, dorsal stylet; 
F, forks of the stylets; Fc, food channel; Hphy, hypopharynx; Lm, labru'm; O, esophagus; 
P, proboscis; Ph, pharynx; Pph, prepharynx; Sc, ventral sac holding the stylets; Sd, sali- 
vary duct; Sg, subesophageal ganglion; VSt, ventral stylet. In d the arrows indicate the 
direction of the passage of blood and salivary fluid. (Redrawn and modified after various 
authors.) 

convex above and has an open slit on the ventral side. Within the haustellum 
are minute denticles (15-16), the buccal teeth. When the louse feeds, these 
denticles are everted and they serve as holdfasts or anchors while the main 
mouth parts are brought into play. The food channel extends from the 
haustellum to the pharynx. Ventral of the food channel and extending to the 
posterior end of the head is a long, narrow diverticulum, which opens an- 



THE ORDER ANOPLURA 199 

teriorly near the buccal plate. Within this divcrticulum lie the piercing mouth 
parts. They consist of dorsal and ventral piercers or stabbers. The dorsal 
stabber is a single stylet; the ventral consists of two stylets closely appressed to 
each other. The piercers resemble long-handled, two-pronged forks, the prongs 
being posterior. Between the dorsal and ventral stabbers lies the salivary duct 
or pipe. All these structures are supplied with a complicated muscular system 

(Fig- 79)- 

METHOD OF FEEDING: When ready to feed, the louse applies its head to the 
skin. By muscular action the haustellum is everted and the teeth are anchored 
in the skin. The stabbers are brought forward, passing into the skin along with 
the salivary duct. Salivary secretion is poured into the wound (Nuttall, 1917, 
has shown that this secretion possesses an anticoagulin), and the pumping 
pharynx (Fig. 79) pumps the blood with great rapidity. The pumping action 
and the passage of the blood into the pharynx and thence to the esophagus and 
intestine can be seen most readily in freshly molted individuals. 3 

THE DIGESTIVE SYSTEM: The digestive system (Fig. 80) consists of a simple 
thin-walled esophagus that opens into a rather large intestine. The mid- 
intestine narrows posteriorly into the hind-intestine at the point of entrance of 
the Malpighian tubules. The hind-intestine curves forward, then backward 
to the anal opening. There is a large rectal ampulla. The salivary glands consist 
of two pairs a pair of tubular glands and a pair of kidney-shaped glands. 
Each gland has a duct that opens independently into the base of the diverti- 
culum containing the mouth parts. Here they connect with the salivary duct 
lying between the stabbers. 

LIFE CYCLE: Adult females of the head louse begin oviposition in from 24 
to ^6 hours after emergence from the last nymphal skin, and each lays, on" an 
average, six to seven eggs a day. The total number of eggs produced by a single 
female docs not seem to be definitely known though Bacot obtained a maxi- 
mum of 141 eggs; Buxton (1946) reports an average of 270 to 300 eggs per 
female. The eggs are cemented to hairs (Fig. 81 A) and are practically 
always deposited with the cap directed away from the base of the hair. They 
measure from 0.9 to i mm. in length. The small, whitish er ~s are usually 
known as "nits." The eggs hatch in from five to nine days when' kept at tem- 
peratures (30 to 35 C.) normal to the habitat of the lice. When ready to 



8 For a full and extended account of the ,niouth parts and their action the reader is 
referred to the works of Harrison, Sikora, Peacock, and Florence. The above account 
is necessarily brief and is abstracted largely from these workers. 



200 MEDICAL ENTOMOLOGY 

emerge the nymph employs a novel method to open the lid or cap of the egg. 
Air is pumped in through the mouth parts and gradually extruded from the 
anus until a cushion of air is obtained of sufficient pressure to force open the 
cap. The fore part of the nymph, which has acted like a stopper, is forced out; 




Fig. 80 (left). Pcdiculus humanus. Internal anatomy of male louse; parts fully labeled. 
(After Nuttall, Parasitology.) 
Fig. 8 1 (right). Eggs of human lice. (A) Pcdiculus humanus. (B) Phthirus pubis. 

pumping continues and the nymph is gradually forced out of the shell. The 
nymph begins feeding promptly within a few hours. There are three molts 
before the adult stage is reached. The length of the life cycle has been accurately 
determined by Nuttall and is as follows: 

Egg stage 7 days 

ist nymphal stage 4 days 



THE ORDER ANOPLURA 20* 

2nd nymphal stage 3 days 

3rd nymphal stage 2 days - 

Total 16 days 

The length of the life cycle may be somewhat prolonged by low temperatures 
or lack of food. The adults live about 30 days. 

THE BODY LOUSE: Pediculus humanus var. corporis dc Geer, 4 the body 
louse, is found principally on the body and oviposits generally on the clothing. 
In practically all characteristics it agrees with capitis, though it averages slightly 
larger in size. About the only distinguishing characters are its habitat and 
its preference for laying its eggs on the clothing rather than on the hairs. 
Nuttall has shown that capitis will oviposit on cloth and that corporis will lay 
its eggs on the body hairs. Such eggs have been found naturally on the body 
hairs of persons infested with this louse. The life history of the body louse is 
very similar to that of the head louse. Nuttall has shown that the female lays 
from 275 to 300 eggs, ovipositing at the rate of about ten a day. The eggs hatch 
in from six to nine days and the entire* life cycle from egg to egg may be as 
short as 16 days. The optimum temj^f rntlirr for its fH^l^p"*" 1 " l ' r 3 n tn y> r:. 

BIONOMICS OF LICE: FEEDING HABITS: The method of feeding has al- 
ready been described. Whereas starved lice will gorge to excess, those present 
on the body feed whenever hungry. They feed most commonly at night or 
yvheruhe host is resting. JThe act of feeding usually occupies three to ten min- 
utes (Nuttall), though other authorities record even as long as two or three 
hours, the lice sucking intermittently. The young lice begin feeding almost 
immediately after hatching, and, if conditions are favorable, continue to 
feed at varying intervals throughout life. As the lice feed and the intestine fills 
with blood, excreta are commonly voided in more or less profusion. This is a 
very important fact when the methods of transmission of pathogenic organisms 
are considered. 

HABITAT: The head louse (capitis) is primarily an inhabitant of the head. 
It may occur and establish itself on other hairy parts, as the beard, pubic 
region, and chest. The body louse (corporis) is largely confined to the clothing 
on which it lays its eggs. Nuttall has recorded a severe infestation of capitis on 
the pubic region. Many observers record the presence of corporis on the body 
and the deposition of its eggs, though not commonly, on the hairs of the breast, 
axillae, perianal, and pubic regions. This is especially true when the infestation 



4 Under the rules of nomenclature this name should be Pediculus humanus humanus 
Linn. 



202 MEDICAL ENTOMOLOGY 

is severe. These observations are of great importance when delousing opera- 
tions are considered. It is useless to delouse by change of clothing after an 
ordinary bath. If the eggs are present on the body hairs, the person will be 
soon as lousy as ever. 

ACTIVITIES: Lice are very active, crawling about with remarkable speed. 
Nuttall observed a female of corporis travel at the rate of one metre in three 
minutes, and it is evident lice can run a distance equal to the length of a man's 
body in a few minutes. 5 They have been seen wandering about rooms, crawl- 
ing up walls, and, not uncommonly, moving about railway carriages and 
'busses. They are more active when warm, corporis climbing more than twice 
as fast at 30 C. than at 17 C. At oC. they are immobile; at 10 C. they move 
slowly; at 20 C. they are fairly active; and at 30 C. they are very active (about 
the temperature of their normal habitat). At 38 to 40 C. they become wildly 
active and soon die from exhaustion. The thermal death point is about 44 C. 
(112 F.). Lice become very active on persons with fever, migrating from the 
patients in large numbers; when a person dies the lice soon abandon the 
body and scatter. These important facts should be remembered when attend- 
ing persons suffering with relapsing or typhus fever. 

Both the head and body lice are very gregarious, tending to congregate in 
large numbers in particular places. This habit may account for the density of 
a primary infestation before active spreading takes place. Nuttall has cal- 
culated that a single female may have 1918 descendants during her lifetime 
(about 30 days), and the offspring of her daughters, during their lifetime, 
would be 112,778, a rather large population to be produced in about 48 days. 

5 It may be well to recall here the poem by Robert Burns entitled, "To a Louse, on 
seeing one on a lady's bonnet at church," in which he described very accurately the 
roaming activities of these creatures: 

"Ha! where yc gaun, ye crowlin' ferlic! 
Your impudence protects you sairly: 
I canna say but ye strunt rarely, 

Owrc gauze and lace; 
Though, faith, I fear ye dine but sparely 

On sic a place. 

"Now haud you there, ye're out o' sight, 
Below the fatt'rils snug and tight; 
Na faith ye yet! ye'll no be right 

Till ye've got on it, 
The very tapmost, towering height 

O' Miss's bonnett." 



THE ORDER ANOPLURA 203 

MODES OF DISSEMINATION AND INFESTATION! It should DC recalled that lice 

are very active, can attach easily to hair or cloth, and cling thereto very 
tenaciously; they can survive for a maximum of ten days without food. Lice 
can readily pass from head to head when in contact; lice, clinging to stray hairs, 
clamber quickly to any warm body surface near at hand; caps or hats worn by 
lousy persons and hung in close contact with others, as in schools and public 
places, undoubtedly serve to spread them. Hairs from lousy persons are often 
scattered in public conveyances, and these falling on other people's clothing 
may start an infestation. Persons suffering from head lice are constantly scratch- 
ing, and hairs bearing nits (eggs) are continually dropping, frequently on 
scats and cushions of railway carriages, busses, etc. Probably the most common 
method of acquiring lice is through contact with infested clothing, bedding, 
brushes, etc. 

THE CRAB LOUSE: Phthirus pubis (Linn.)., the groin, pubic, or crab 
louse (Fig. 82), is a very distinctive louse. It is usually confined to the pubic 
and perianal regions, though it is recorded from the head, eyebrows, eyelashes, 
the axillae, breast, and beard. Herms records seeing soldiers infested from 
their ankles to their necks, and Nuttall also observed similar conditions among 
soldiers he examined in England. However, the main site of infestation is the 
pubic and perianal region. The prevalence of this louse among the general 
population is not known. Grccnough (1888) records that in the examination of 
864 verminous patients admitted to a hospital in Boston 3 per cent were 
infested with the crab louse. From personal knowledge the author is led to 
believe that this louse is quite widely prevalent, but very few records are kept. 
It is restricted to man as a host, though there are some records of dogs being 
infested. Further investigation is needed to learn whether the clog may be a 
normal host and serve as an animal reservoir of this louse. 

The crab louse is grayish white in color; it measures 1.5 to 2 mm. in length 
and is nearly as broad as long. It remains almost immobile upon the host, 
the hind legs grasping two hairs. In this position it continues to feed inter- 
mittently for hours or clays, rarely removing its mouth parts from their 
position in the host. During its entire life it remains near its first point of 
attachment, withdrawing its mouth parts only at the time of molting. As it 
feeds it defecates frequently, voiding blood and wastes intermingled. This 
frequent defecation soon renders its surroundings filthy. 

LIFE CYCLE: Nuttall gives an excellent account of the biology of this species. 
Mating takes place on the host and the eggs (Fig. 81 B) are deposited on the 
hairs, close to the base. The total egg production of a single female has not been 



204 MEDICAL ENTOMOLOGY 

accurately determined, though Nuttall records 26 eggs laid by one during a 
period of 12 days (the female died 17 days after reaching sexual maturity). The 
eggs hatch in from 7 to 8 days. The young nymph attaches within a few hours, 
and the first molt takes place in from 5 to 6 days; the second molt in 9 to 10 
days; and the third molt in from 13 to 17 days. The complete life cycle from 
egg to egg occupies from 34 to 41 days. The -nymphs or adults cannot survive 
very long when removed from the host, a maximum of two days being 
recorded. 




Fig. 82. The pubic louse, Phthirus pubis. Female. 

DISSEMINATION: The crab louse is usually spread during coitus, but there 
are many other ways in which persons may become infested. Some of these 
are the use of common or piled bath towels in dormitories, gymnasiums, etc.; 
contact with hairs bearing eggs or lice that may drop on clothing, bedding, 
the seats of public toilets, etc., as the result of scratching by infested persons; 
the throwing or piling together of undergarments, athletic suits, etc. Under 
crowded conditions a single infested individual may distribute them to an 
entire family or group of people with whom he or she comes constantly in 
contact. 



THE ORDER ANOPLURA 205 

LICE AND DISEASE 
HEAD AND BODY LICE 

The head and body lice of man affect him in two principal ways: through 
the direct effects of their bites and by the transmission of pathogenic or- 
ganisms. 

BITES : The bites of lice have a very marked effect on most people, though 
some persons are apparently immune to their attacks (Moore and Hirsch- 
felder record an experimental individual on which lice refused to feed) and 
others become immune after continued attack. The bites produce minute hem- 
orrhagic spots, which are found most frequently over the neck, back, breast, 
and abdomen. These spots are accompanied by an urticaria, often with intense 
itching, leading to scratching and frequent secondary infection. Among persons 
(as tramps, vagabonds, chronic drunkards, and children living under filthy 
conditions) who harbor lice for years, the skin back of the head, over the 
breast, and on the neck, back, or any part frequently bitten becomes roughened, 
thickened, and deeply pigmented (melanoderma), producing what is com- 
monly called "vagabonds' disease." As the body louse attacks most frequently 
at night or when the host is resting, it causes a great deal of irritation, loss of 
sleep, and restlessness, which may induce irritability and an anemic condition, 
especially in children. Insomnia and neurasthenia may result from continued 
infestation. Moore (1918) records rather severe effects from the experimental 
feeding of lice on himself. After feeding 700 to 800 lice twice each day, he 
developed almost at once a tired feeling, an irritable and pessimistic state of 
mind, and an illness resembling grippe with a body rash. All these effects rap- 
idly disappeared when the lice were removed and feeding discontinued. 

DISEASES : There are at least three important human diseases transmitted 
by lice: (i) epidemic typhus; (2) trench fever; and (3) relapsing fever. An- 
other disease, endemic typhus or murine typhus, is mainly associated with rats 
and rat parasites, since fleas and mites are the transmitters among rats and 
to man (see pp. 98, 560) ; human lice are also capable of acting as vectors. 

EPIDEMIC TYPHUS, OLD WORLD TYPHUS, JAIL FEVER, TYPHUS EXANTIIEMATICUS, 

LOUSE TYPHUS, ETC.: Typhus is an acute infectious disease caused by Ricfatsia 
prowazety da Rocha-Lima (1916) and is transmitted by the human louse, 
Pediculus humanus Linn. The disease is characterized by sudden onset, high 
fever, severe headache, and marked prostration, followed on the fourth or fifth 
day by a pinkish body rash. The course of the disease is rapid, a fall in tempera- 



20 6 MEDICAL ENTOMOLOGY 

ture occurring on the twelfth to the fourteenth day, followed by a rapid recovery 
or death. The mortality rate varies from 5 per cent to as high as 70 per cent in 
severe epidemics. 

Typhus fever is world-wide in distribution and may occur wherever human 
lice are abundant. Epidemics have occurred in most parts of the world. It is 
prevalent principally in the cooler climates where people are compelled to 
wear heavy clothing and bathing and clothing changes are infrequent. Out- 
breaks are most frequent in the winter because of the crowding of the poorer 
classes, bad sanitary conditions, and lack of adequate food, inducing general 
debility. The disease is practically always associated with poverty and unsani- 
tary living conditions or, under war conditions, with famine, national poverty, 
political upheavals, or revolutions. Severe epidemics occurred during World 
War I in Serbia, Romania, and Poland, and the aftermath witnessed severe 
outbreaks in Poland and Russia. In World War II epidemics threatened in 
areas overrun by the various armies as in Italy and North Africa, but these 
were soon halted by the use of DDT. 

That lice are the transmitters of typhus was first demonstrated by Nicolle 
and his associates in 1909 in Tunis, North Africa. They succeeded in transmitt- 
ing typhus from infected monkey to uninfected monkey by body lice. These 
results were fully confirmed by Ricketts and Wilder (1910), Goldberger 
(1912), and others in various parts of the world. These workers stated that the 
transmission was by the bites of the louse; this is now known not to be the 
case. The causative organism was discovered by da Rocha-Lima (1916), and 
the complicated method of transmission by lice has since been fully elucidated. 
Man is believed to be the reservoir of the disease. Lice feeding on typhus pa- 
tients ingest the rickettsiae that are in the circulating blood during the febrile 
period (the third to the loth day). In the lice the rickettsiae invade the epi- 
dermal cells lining the stomach and mid-gut; here they multiply in enormous 
numbers and cause the cells to burst and liberate them. This developmental 
cycle requires from five to nine days. The infected louse now feeds on a new 
patient and infection may occur in one of three ways: (i) the louse in feeding 
defecates and the rickettsiae in the feces may enter the wound or the abra- 
sions that result from scratching; (2) the louse is crushed by the patient and 
the" contents of the intestine of the louse are spread over the skin to enter 
wounds or scratches; (3) the feces of infected lice may fall on mucous mem- 
branes about the eyes, the mouth, or other exposed mucous surfaces. In addi- 
tion, it has been demonstrated that, though infected feces may become dry and 
powdery, the rickettsiae are still infective and may be scratched into the skin 
or rubbed on mucous surfaces or they may be air-borne and gain access to 



THE ORDER ANOPLURA 207 

mucous surfaces (from feces contaminating bedding, clothing, and so forth). 
The rickettsiae in man invade the cytoplasm of the cells, and the incubation 
period varies from 8 to 12 days. No successful treatment is known. At present 
a fairly effective vaccine has been developed from killed rickettsiae and is 
being used with considerable success. The prevention of infection is of the 
greatest importance in controlling or preventing an outbreak. This involves 
effective louse control (see pp. 211-213), cleanliness, improved living condi- 
tions, adequate bathing and laundering facilities, and the prevention of louse- 
infected people from entering the areas. 'Mass vaccination is of importance 
where it can be done effectively. There is no known animal reservoir of 
epidemic typhus except man. However, the monkey lice (Pedicinus longiceps 
and P. albidus) have been shown capable of transmitting the disease to 
monkeys and the rat louse, Polyplax spinulosa, of transmitting the disease 
among rats. The rickettsiae are not known to be transmitted by lice to their 
young (in fact most infected lice are said to die). The sources of epidemic out- 
breaks are not known. 

BRILL'S DISEASE: Although generally regarded as a form of murine or endemic 
typhus, Brill's disease has been shown to be a mild form of epidemic typhus and 
is transmitted by the human louse. 

ENDEMIC TYPHUS, MURINE TYPHUS, OR FLEA TYPHUS: This is a mild typhuslikc 
disease caused by Ric\ettsia mooseri (typhi} and is transmitted to man by the 
bites of infected fleas, infective flea feces, or the eating of food contaminated 
by urine from infected rats. The body louse, Pcdicidus humanus corporis, can 
also transmit the disease. 

That rats (the brown rat, Rattus norvegicus, and others) and probably mice 
are the reservoirs of the rickettsiae has been well demonstrated by Dyer, 
Rumreich, and their associates (1931, 1932), 'Mooser and his co-workers in 
Mexico, and many others. More recently Brigham (1937) has isolated a strain 
from a field mouse (Peromy setts polionotus polionotus) from a rural district 
in southern Alabama, and the same author (1937) has shown mice, various 
species of rats, flying squirrels, cotton mice, golden mice, and wood rats 
to be susceptible to infection. Among rats the vectors are fleas (Xenopsylla 
cheopis, Nosopsyllus jasciatus, and probably others), the rat louse (Polyplax 
spinulosa), and the tropical rat mite (Liponyssus bacoti). Brigham (1941) re- 
covered a strain of typhus from the sticktight flea, Echidnophaga gallinacea, 
collected from rats in Georgia, and Alicata (1942) transmitted endemic typhus 
by this flea. 

The disease in man (apparently it has little effect on rats or other rodents) 



2 o8 MEDICAL ENTOMOLOGY 

is mild, and the death rate is less than 5 per cent in the United States. In man 
the incubation period varies from 6 to 14 days followed by fever and a rash. 
Recovery normally occurs in two or three weeks. Eskey (1943) reports some 
20,000 cases in the United States from 1932 to 1941 but indicates that this was 
probably less than 20 per cent of the actual cases. As the main source of human 
infection is rats, the control or eradication of these pests would practically 
eradicate the disease. 

Murine typhus is widely distributed in the southern United States, extend- 
ing northward into New York, Ohio, Iowa, and California; it is widespread 
in Mexico, parts of South America, Africa, southern and western Europe, the 
Near East, eastern Asia, and nearby areas. 

TRENCH FEVER: Trench fever, or Volhynia fever, was first diagnosed as a 
clinical entity in 1915 during World War I. It is believed to be caused by 
RicJ^ettsia quintana (R. tvolhynicd), but this has not been definitely proved. It 
is a specific relapsing fever transmitted to man by the body louse, Pedicttlus 
humanus corporis, through the infected feces only. It is not transmitted by the 
bites of infected lice, nor is it known to be transmitted through the eggs. 
During World War I trench fever is said to have caused about 25 per cent of 
all cases of illness in the British Army in France and the disease was very 
prevalent in the German and Austrian Armies. Byam (1923) reports 800,000 
cases among the Allied armies in France during the four years of the war. 
Outbreaks occurred in Egypt and Mesopotamia as well as in Europe. During 
World War II the disease was rare. 

In man the organism of trench fever is present in the blood, and the blood 
is infective to lice from the first day of the disease. In lice there is a develop- 
ment period of five to nine days before the excreta are infective. The louse 
remains infective as long as it lives. The excreta retain their virulence for a 
long time, at least four months. Man becomes infected by scratching the 
excreta into the injured skin, crushing the lice, or in any way that brings the 
infective fecal wastes into the blood stream. In man the incubation period 
varies from 10 to 30 days (Mackie et aL, 1945). The onset is sudden with 
severe headache, weakness, vertigo, and fever of 103 to 104 F. The fever 
soon subsides (one to two weeks) and is followed by several relapses (three 
to five). During the disease there is usually a rash on the chest, back, and 
abdomen. Recovery is slow (frequently prolonged) and the sequelae are, in 
many cases, serious. A s there is no successful treatment, the control of lice is 
very important. In man there is only a fleeting immunity and reinfection may 
occur within six months. 



THE ORDER ANOPLURA 209 

RELAPSING FEVER: There are two types of this disease, tick-borne (see pp. 
71-73) and louse-borne. Species of Spirochaeta are the causative agents of 
the disease, but no agreement seems to have been reached as to the species 
concerned. Spirochaeta recurrent!* (Lebert) is usually regarded as the louse 
species. There is doubt about the possibility or probability that tick-borne 
species can also be transmitted by lice or vice versa. The two diseases, typhus 
and louse-borne relapsing fever, frequently occur about the same time in the 
same areas, or they may be separated by a few years. Mackie (1907) first 
demonstrated that the body louse (Pediculus hunt anus corporis] served as the 
vector in India in an area where typhus had never been recorded. This work 
was confirmed by many investigators in North Africa and other parts of the 
world. According to Chung and Feng (1936), the developmental cycle in the 
louse is as follows. The louse feeding on a patient obtains the spirochetes in its 
blood meal. Most of the ingested spirochetes are soon digested, disappearing 
within six to eight hours. A few, however, penetrate the wall of the intestine 
and appear in the coelomic fluid in about two hours, and numbers are seen 
within eight hours. At the same time dead spirochetes appear in the feces. 
Within the body cavity the spirochetes multiply by transverse division and 
soon appear in all parts of the body. They do not invade the tissues nor are 
they transmitted through the egg or through the feces. Within the louse the 
spirochetes persist as long as the louse lives (19 days or more). Infection of 
man takes place by crushing the lice directly on the skin by the fingers or 
other means, whereby the spirochetes gain entrance through abrasions, or by 
scratching, thus permitting their access to the blood. The vectors are both the 
body and head lice. 

Relapsing fever has occurred in epidemic form in most parts of the world. 
It is associated with lousiness in jails, armies, overcrowded and poverty stricken 
areas, famines, wars, and political disturbances. ^Though the clinical entity of 
the disease was recognized in the early part of trie nineteenth century, it was 
not till 1873 that the etiological agent was described by Obermeier and named 
Protomycetum recurrentis by Lebert in 1874, now called Spirochaeta recur- 
rentis (Lebert) . Epidemics have been recorded from many countries and cities 
as in Dublin (1739 and later), parts of Scotland (1842-1844 and later), Eng- 
land (1847-1848 and later), Russia (1833, 1863, and later), Germany (1868 and 
later), most of Asia, Egypt (1851, 1884, and later), most of India (1852 and 
later), North Africa, West, central, and parts of East Africa (to the present 
time) and China; it is not known from Australasia. The disease has been 
recorded from the eastern coastal cities of North America (1844, 1847, 1871) 



210 MEDICAL ENTOMOLOGY 

but is apparently absent at the present time. It also occurs in some parts of 
South America. 

During and after World War I great epidemics swept over Poland, central 
Russia, Romania, and Serbia. In Romania alone there were over one million 
cases of typhus and more of relapsing fever in a population of five million. 
The most recent great epidemic swept over central Africa, appearing first 
in French Guinea in 1921, and gradually spread southward to Nigeria, east- 
ward to the Anglo-Egyptian Sudan, and northward to various areas. By 1928 
it had subsided, though during the epidemic it is estimated about 10 per cent 
of the population died. In French Sudan and the Niger area over 80,000 died 
within two years. (Scott, 1939). Though some of the newer arsenical drugs 
appear to act effectively in the cure of relapsing fever, yet the most important 
measure is the control of lice. Where lice are adequately controlled, louse-borne 
diseases soon disappear. 

OTHER LICE 

Phthirus pubis has not, apparently, been extensively experimented with as 
an agent in the transmission of disease. "It is not known to serve as a vector of 
any infective disease" (Nuttall, 1918). Todd (1922) states that it may transmit 
relapsing fever. The main effects of this louse are local. Pruritus is usually the 
first symptom and leads to scratching and secondary infections. With many 
persons no ill effects are evident though pale bluish-gray maculae mark the 
sites of the bites. 

Another interesting relation of lice (other than human lice) to man is 
that a species of dog lice, Trichodectes canis de Geer 6 (a species of Mallo- 
phaga), serves as the intermediate host of the dog tapeworm (Dipylidium 
caninum Linn.). This tapeworm is found occasionally in man, particularly 
children. The dog harbors the tapeworm, and the defecated proglottids with 
their eggs become entangled in the hairs of the host. If these eggs are de- 
voured by the lice, the cysticercoid stage develops in them. The dog becomes 
infected by swallowing the infected lice. Persons handling and petting infected 
dogs may accidentally become infected through swallowing a louse contain- 
ing the cysticerci. This most commonly occurs with children that play 
with dogs harboring this species of tapeworm. 

Another interesting relation is that of the rabbit louse, Haemodipsus ventri- 
cosus Denny (Siphunculata). Francis (1921) showed experimentally that this 



6 Other intermediate hosts are the dog and cat fleas (Ctenocephalides canis and C. felts) 
and the human flea (Pulex irritans). 



THE ORDER ANOPLURA 211 

louse is an active agent in the dissemination of tularemia (Bacterium tularense) 
from rabbit to rabbit. This is undoubtedly one of the means by which this 
disease is transmitted in nature, and it thus aids in maintaining a natural 
reservoir from which man may become infected. 

CONTROL OF LICE 

The problem of the control of lice may well be discussed under two distinct 
heads: (i) personal cleanliness and debusing; (2) public cleanliness and mass 
debusing. 7 

DELOUSING OF THE INDIVIDUAL 

PERSONAL CLEANLINESS: Personal cleanliness is probably the most 
effective measure against lousiness. However, the religion of cleanliness, both 
personal and public, has not become universal, and there still exists, among 
all peoples and nations, a proportion of the population that may be called "the 
great unwashed." Unfortunately, cleanliness is not always a concomitant of 
what may be called a rising civilization. Furthermore, there are many super- 
stitions in regard to lice, their presence being taken to indicate good health, 
vigor, fertility, protection against disease, 8 etc. Owing to the dangers of disease 
transmission, everyone should take the utmost precaution against infestation. 
Certain simple rules should be followed as far as possible: (i) avoid all con- 
tact with lousy persons and their effects; (2) avoid overcrowding whenever 
possible; (3) bathe at least once a week, using plenty of hot water and soap, 
and rub dry with a rough towel; (4) wear underwear at all times and make 
a complete change at least once each week ; to use no underwear is an unclean 
habit and invites lousiness; (5) wash the head carefully at frequent intervals; 
comb and brush it at least once a day and keep it clean at all times; (6) avoid 
unclean bedding, especially blankets; when traveling, carefully inspect the 
bedding before retiring; (7) carefully inspect the head and body at frequent 



7 Lousing is the correct term to use in this connection but it has fallen into disuse, 
owing, no doubt, to the decreasing lousiness of peoples. To louse, according to the Oxford 
English dictionary, means "to clear of lice, to remove lice." "Howe handsome it is to lye 
and sleepe, or to lowze themselves in the sunshine" (Spenser, View of the Present State 
of Ireland, 1633). "To York House, where the Russian Ambassador do lie; and there 
I saw his people go up and down lousing themselves" (Pepys* Diary, June 6, 1663). 
(From Nuttall.) 

8 "Ten lice boiled in milk with plenty of salt and taken on an empty stomach was 
certain to cure jaundice, a very common complaint among the Lapps in Spring" (The 
Story of San Michele by Axel Munthe). 



212 MEDICAL ENTOMOLOGY 

intervals, especially if you have been exposed to contacts with lousy individ- 
uals; (8) in case of infestation, vigorous treatment should be adopted at once. 

HEAD LICE (P. humanus capitis) : In mild infestations the lice and the nits 
(eggs) can be removed by hand picking and vigorously combing with a fine- 
toothed comb. Frequent washing and combing will usually eliminate a mild 
infestation. If lice are abundant or even if only a few, they can be quickly 
destroyed by one of the newer lousicides. A 10 per cent DDT (by weight) in 
some carrier as pyrophyllite is very effective. Dust the head thoroughly (about 
a spoonful of the powder) and rub the dust in vigorously with the hands. Also 
rub some into the eyebrows and beard (if present); avoid getting any into 
the eyes. The head should not be washed for 24 hours or longer. This will 
kill all the lice but not the eggs. Use the same treatment a week or ten days 
later to kill any lice that have hatched. Two thorough treatments even on 
heads with dense hair will eliminate lice. Another treatment is by the use 
of liquid solutions of DDT. When using these, follow carefully the directions 
of the manufacturer as given on the containers. 

BODY LOUSE (P. humanus corporis) : As this louse is found mainly on the 
clothing, a thorough treatment of the clothing, especially the underwear, is the 
most effective method. Sift a 10 per cent DDT powder thoroughly over 
the insides of the underwear, carefully rubbing it into all the seams. Apply the 
same treatment to the insides of trousers (in the case of women, treat the insides 
of skirts), shirts, and caps. If such garments arc worn without washing, a 
single treatment is good for three weeks. If washed in warm soapy water, the 
clothing will still be effective for a short period. If new infestation is avoided, 
a single treatment should be effective. In case of constant exposure to infesta- 
tion, as on the part of nurses, social workers, medical officers, or others work- 
ing among lousy persons, especially when typhus or relapsing fever is prev- 
alent, the underclothing may be impregnated with a DDT emulsion or 
DDT may be mixed with a dry-cleaning fluid. Such emulsions can be prepared 
or purchased. 

CRAB LOUSE (Phthirus pubis) : This louse may be controlled by dusting the 
groin region, the arm pits, or other hairy portions of the body with a 10 per 
cent DDT dust. Rub in thoroughly and do not bathe for at least twenty-four 
hours. Follow with a second treatment in a week to ten days to kill any lice 
that have hatched. 



THE ORDER ANOPLURA 213 

MASS DELOUSING 

In armies or among lousy populations it is often necessary to use mass 
delousing methods. These methods were developed and refined during World 
War II. The simplest method used in Naples, Italy (1943-1944), to control an 
epidemic of typhus was the use of DDT as a 10 per cent dust (by weight). By 
means of small hand blowers the dust was blown between all layers of the 
clothing, particular attention being paid to undergarments. This was accom- 
plished by blowing down the back, down the front, up the sleeves, down the 
trouser legs, and up the legs to cover the entire body and clothes with the dust. 
If such dusted clothing is worn for a week or longer, all the lice and those 
hatching from eggs will be destroyed. Such a mass delousing can be carried 
out effectively only under police regulations acting under the orders of the 
medical authorities. 

To carry out a mass delousing program requires legal regulation, for it 
necessitates not only destroying the lice on the persons but also those on dis- 
carded or recently worn clothing. This may be carried out effectively by organ- 
izing definite delousing stations, as is done by the Army and Navy and at 
ports of entry to any country. In such a station arrangements are made 
that all worn clothing in addition to those on the individual must be 
brought. All such clothing, including what is worn, is placed in a gastight bag 
in which is placed the required amount of methyl bromide in glass ampoule, 
or the clothing is labeled and placed in gastight chambers for treatment with 
methyl bromide. In the bag the ampoule is broken, and in 45 minutes the bag 
may be opened and the clothes taken out and shaken. They are now ready 
for wear. In the gas chambers masses of clothing can be treated. While the 
clothing is being treated, the unclothed individuals may take a bath. They 
arc then sprayed with a lousicide such as the NBIN formula (see p. 103) used 
by our Army and Navy. The individual now receives his clothing, all the lice 
on his body and his clothing having been killed. By such a method 400 to 500 
can be treated each day in a small station; larger units can handle more. In 
addition, mobile units can be used where isolated groups have to be treated. 

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214 MEDICAL ENTOMOLOGY 

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**Nuttall, G. H. G. Bibliography of Pediculus and Phthirus. Parasitology, 10: 

1-42, 1917. 
. The part played by Pediculus humanus in the causation of disease. Ibid., 

pp. 43-79, 1917. 

. The biology of Pediculus humanus. Ibid., pp. 80-185, 1917. 

. The pathological effects of Phthirus pubis. Ibid., pp. 375-382, 1918. 

. The biology of Phthirus pubis. Ibid., pp. 383-405, 1918. 

. Combating lousiness among soldiers and civilians. Ibid., pp. 411-586, 

1918. 

. The biology of Pediculus humanus. Ibid., 11: 201-220, 1919. 

. The systematic position, synonymy, and iconography of Pediculus humanus 

and Phthirus pubis. Ibid., pp. 329-346, 1919. 
. On Fahrenholz's purported new species, subspecies, and varieties of Pedi- 

culus: a criticism of methods employed in describing Anoplura. Ibid., 12: 

136-153, 1920. 
Peacock, A. D. The structure of the mouth parts and mechanism of feeding in 

Pediculus humanus. Ibid., n: 98-117, 1918. 
Shattuck, G. C. Typhus fever in Boston and a review of the newer methods of 

diagnosing typhus. Amer. Jl. Trop, Med., 2: 225-250, 1922, 



THE ORDER ANOPLURA 217 

Sikora, H. Beitrage zur Biologic von Pediculus vestimcntl. Central. Bakt., I 
Abt., Orig., 76: 523-537, 1915. 

. Beitrage zur Anatomic, Biologic und Physiologic der Kleiderlaus (Pedi- 
culus vestimenti Nitzsch.) i. Anatomic des Verdauungstraktus. Arch. Schiflf. 
Trop. Hyg., 20: 5-76, 1916. 

Sobel, }. Pediculosis capitis among school children. New York Med. Jl., 98: 
656-664, 1913. 

Strong, R. P. Trench fever report of Commission, Medical Research Committee, 
American Red Cross. New York, 1918. 

Topping, N. H., and Dyer, R. E. Apparent extension of typhus in the United 
States. Amer. Jl. Trop. Med., 23: 37-42, 1943. 

U.S. Department of Agriculture. DDT and other insecticides and repellents. 
Mis. Pub. No. 606, 1946. 

Wolbach, S. B., Todd, J. L., and Palfrey, F. W. The etiology and pathology 
of typhus; being the main report of the Typhus Research Commission of the 
League of Red Cross Societies to Poland. Cambridge, Mass., 1922. 

Zinsser, H. Rats, lice and history. Boston, 1935. 

. The rickettsia diseases: varieties, epidemiology and geographical distribu- 
tion. Amer. Jl. Hyg., 25: 430-463, 1937. 



CHAPTER VIII 



The Diptera: Flies 



^ I ^HE Diptera are insects with only one pair of membranous wings (in 
JL some groups the wings are lacking or vestigial) which are borne by the 
mesothorax (Fig. 83); the second pair of wings is represented by a pair of 
short, knobbed, filiform organs, the halteres (Fig. 53). The mouth parts are 
suctorial, usually forming a proboscis and, in some groups, adapted for pierc- 
ing. The larvae are legless and their respiratory system is reduced (generally 
amphipneustic) ; the pupae are usually free or enclosed in the last larval skin 
(puparium). The metamorphosis is complete. 

The Diptera constitute a very large order: over 80,000 species have been 
described from the world and at least 10,000 from North America. Many 
of the species are very abundant in individuals and are world-wide in distribu- 
tion. Furthermore, they vary extremely in their habits both as larvae and as 
adults. The adults are mainly diurnal, feeding on nectar, the exudates from 
plant and animal wounds, or decaying animal or vegetable matter; some arc 
predaceous, as the robber flics (Asilidae), while large groups, and sometimes 
almost entire families, have acquired the bloodsucking habit and attack a 
great variety of hosts. The larvae may be scavengers, as the blowflies, flesh 
flies, bluebottle flies, etc., parasites on man and animals, as in the myiasis- 
producing flies (see pp. 492-533), or parasites on other insects (all the Tachini- 
dae, some of the Sarcophagidae, etc.). Many are injurious to man's crops; others 
are beneficial, destroying noxious insects (the larvae of the Syrphidae are usu- 
ally predaceous and feed on a great variety of insects; those of the Tachinidae 
are also beneficial) ; while many others feed on wastes of all kinds and, in many 
cases, are highly beneficial. 

The bloodsucking habits of the adults; the propensity of many flies to 
feed on fecal or decaying wastes and human and animal foods; their search 
for moisture on mucous membranes, exudates from sores, wounds, or dis- 
charges from diseased tissues; and the domestic habits of many species all 
render the group of great importance to man. In addition to these extremely 



THE DIPTERA: FLIES 219 

annoying habits, many flies, both bloodsucking and nonbloodsucking, are now 
known to be the vectors or hosts in the developmental stages of many parasites 
pathogenic to man and animals. Here may be mentioned mosquitoes and 
malaria, yellow fever, dengue, filariasis, encephalitis (and other diseases); 
Glossina flies and sleeping sickness or trypanosomiasis; houseflies and typhoid 
fever, diarrheas, (and other diseases); Phlebotomus flies and Oroya fever, 
kala azar, and pappataci fever. Viewing the group as a whole we may roughly 




Fig. 83. A common flesh fly, Sarcophaga bullata. A, arista of antenna; Al, axil- 
lary lobe; MES, mesonotum, which occupies practically all of the dorsal surface 
of the thorax; O, ocelli; SCT, the scutellum of the mesonotum; TS, transverse 
suture. 

classify the disease relationships of flies to man and animals in the following 
categories : 

1. Flies, bloodsucking in habit, act as carriers of pathogenic organisms. The 
carriage may be mechanical, that is, the fly feeding on the blood of a diseased 
animal may go directly to another susceptible animal to complete its meal and 
inoculate living organisms present in or on its proboscis; the fly may also act as 
a host in the developmental cycle of the organism, as mosquitoes do in malaria. 

2. Flies, nonbloodsucking in habit, may deposit their eggs or living larvae in 
wounds, sores, cavities, on the surface or hairs of the body, or on food, and the 



220 MEDICAL ENTOMOLOGY 

larvae developing cause serious diseased conditions (myiasis-producing larvae) . 

3. Bloodsucking and nonbloodsucking flies may act as the intermediate 
hosts of helminths of man and animals. Examples: Culex fatigans and Wuche- 
reria bancrojti of man; Culex pipiens, Aedes vexans, etc., and Dirofilaria im~ 
mitis of dogs; Simulium damnosum, S. metallicum, and Onchocerca volvulus 
of man; Chrysops spp. and Loa ha of man; Musca domestica and Choano- 
taenia infundibulum of poultry; and many others. 

4. Nonbloodsucking flies that seek moisture about mucous membranes, 
either diseased or not, or that feed on fecal or other human or animal wastes, 
liquids, or discharges from wounds may distribute pathogenic organisms on 
their bodies or by way of their intestinal tracts. The organisms obtained with 
the food may be digested but, if not, may be passed with the feces or the so- 
called "vomit spots" of many flies. A large number of flies are involved in these 
relations and our knowledge of them is far from complete. 

STRUCTURE 

The structure of the Diptera can be dealt with only very briefly, and then 
only those characters mainly concerned with classification and in the transmis- 
sion of disease can be treated. 

THE HEAD (Figs. 83,84) : In flies the head is free and movable and usually 
of relatively large size. It bears the large compound eyes which may be con- 
tiguous on the vertex (holoptic) or widely separated (dichoptic). Ocelli are 
generally present and usually three in number, located between or slightly 
behind the eyes on the vertex. The antennae are of varied forms (Fig. 51) and 
furnish excellent characters for classification. The mouth parts are formed for 
sucking (Fig. 47), lapping, or piercing (Fig. 97). Their structure varies greatly 
in the different families and details will be given in the treatment of those 
families (for a general account see pp. 133-139). In the specialized Diptera 
(suborder Cyclorrhapha) there will be observed a small inverted U-shaped 
suture immediately above the antennae, the frontal suture (Fig. 84). This 
suture represents the opening through which the ptilinum, a bladderlike struc- 
ture, was extruded at the time the adult emerged from its puparium. The ptili- 
num is forced out by internal pressure and the cap of the puparium is broken 
off; its usefulness now ended, it is withdrawn into the head and the frontal 
suture marks the point of withdrawal. The median area extending from the 
frontal suture to the ocelli and lying between the rows of bristles (frontal 
bristles) is the frontal vitta. A small area above and between the bases of the 
antennae is known as the frontal lunule. 



THE DIPTERA: FLIES 




Fig. 84. The areas and setae of the head of the blowfly, CaUiphora viridesccn 
(After Walton.) 



222 MEDICAL ENTOMOLOGY 

THE THORAX: the thoracic region is largely composed of the meso- 
thorax, both the prothorax and metathorax being greatly reduced (Fig. 85) . 
The interpretation of the various sclerites of the thoracic region is still much 
in dispute so that conventional terms, with no special morphological value, are 
widely used. This is especially true of the terms used to designate the various 
groups of bristles or macrochaetae (Fig. 85). The wings of the Diptera consist 
of a single pair, the second pair being reduced and represented by the halteres. 
The wings are thin and membranous, usually naked or with microscopic setae. 
In the Psychodidae (moth flies) the wings are covered with fine hairs, while 
in the Culicidae (mosquitoes) the margin of the wing bears a fringe of scales 
and most of" the veins are also scaled (Fig. 93). The venation of the wings is 
much used in the classification of this order. It corresponds rather closely to 
the hypothetical type (Fig. 55). The names applied to the veins and the cells 
will be found on pages 145-149. Fig. 86 shows in detail the modifications found 
in the more specialized Diptera (Muscidae) with all the veins and cells fully 
labeled. 

In many families the posterior margin of the wing, near its base, is 
notched, the axillary incision; the lobe thus somewhat detached is called the 
posterior or axillary lobe (Fig. 86). In addition, the axillary lobe may be 
greatly expanded (many muscoidean flies) and folded beneath the wing base. 
When fully developed there are two extra lobes, one above the other (Fig. 
83). These lobes are called the calypteres, alulae, or squamae, and are desig- 
nated the upper and lower respectively. 

The legs vary greatly in length and stoutness. They consist of the usual 
parts (Fig. 54). The tarsi are usually five-jointed and may terminate in pul- 
villi. Between the pulvilli there often exists a third structure, the empodium, 
which may be bristlelike or padlike. 

From the standpoint of taxonomy the wing venation, antennal characters, 
and the arrangement of the bristles of the head, thorax, and at times the 
abdomen constitute very essential characters. The arrangement of the bristles 
are of especial importance in many of the groups of Diptera that are of great 
interest to the medical entomologist. 

CHAETOTAXY OF THE DIPTERA 

Muscoidean Flies (Myodaria) 
THE HEAD: 

The arrangement of the bristles and the parts on which they occur are 
fully illustrated in Fig. 84. A frontal view and a lateral view of the head are 
shown in the two upper figures and all the bristles are named. These are: 



THE DIPTERA: FLIES 223 

/. Facial Bristles: A series of bristles on each side borne by the vibrissal 
ridge, above the vibrissae. 

2. Frontal Bristles: A row of bristles on each side of the frontal vitta; the 
lower ones directly above the frontal suture or base of the antennae are 
often called the trans jrontals ; and the upper one to four, the frontals. 

3. Pronto-orbital Bristles: One or several bristles, usually in a row, be- 
tween the frontal bristles and the eye. They are located on the genovertical 
plate. 

4. Lateral Facial Bristles: One or two bristles at times present on the 
sides of the face below the eye (marked "sometimes called cruciate" in the 
figure). 

5. Ocellar Bristles: A pair, the greater ocellars, are situated on the ocellar 
triangle just back of the median ocellus; they always point forward and 
diverge. The lesser ocellars are small bristles located in lines back of the 
greater ocellars and consist of a variable number. 

6. Vertical Bristles: Two pairs, an inner and outer pair, situated on the 
vertex and inserted more or less behind the upper and inner corners of the 
compound eye. 

7. The Vibrissae: A pair of stout bristles, one on each side of the lower 
part of the face, near or above the oral margin. 

8. The Beard: The beard is represented as a mass of fine bristles present 
on the lower portion of the occiput and cheek. 

9. The Arista: A prominent bristle, arising from the third segment of the 
antennae. It may be bare, partially or completely plumose, or modified in 
other ways (Fig. 51). 

The parts of the head on which the above-described bristles are borne are 
fully explained in the figure. 

THE THORAX (Fig. 85) 

THE SUTURES AND RECiIONS: The following sutures of the thorax 
are of importance in determining areas of the thorax: 

1. The Transverse Suture is an impressed line extending across the meso- 
notum, terminating a little in front of the root of the wing. 

2. The Notopleural or Dorsopleural Suture extends from the humeral 
callus to the mesopleural suture and separates the mesonotum from the 
pleuron. 

j. The Mesopleural Suture extends downward from in front of the wing 
to the sternopleural suture, separating the mesopleuron from the pteropleu- 



224 MEDICAL ENTOMOLOGY 

4. The Sternopleural Suture separates the mesopleuron from the sterno- 
pleuron. 

The areas bounded by these sutures are all named in the lateral view of the 
thorax (Fig. 85). 

THE THORACIC BRISTLES: The bristles of the thorax and their ar- 
rangement are of great importance and a mastery of them is essential for 
any systematic work with the higher Diptera. Their importance is also 
accepted in other groups (Culicidae, etc.). The more important bristles are: 

1. Acrostichals: Two rows of bristles, one on each side of the median line 
of the mesonotum. The transverse suture separates them into the anterior 
and posterior acrostichals. 

2. Dorsocentrals: A row on each side, next to and parallel with, the acrosti- 
chals. The transverse suture divides them into the anterior and posterior 
dorsocentrals. 

j. Discal Scutellars and Marginal Scutellars: The discal scutellars usually 
consist of a pair of bristles on the dorsal portion of the scutellum; the mar- 
ginal scutellars form a distinct row of large bristles on the margin of the 
scutellum. 

4. The Humerals: One or more bristles situated on the humeral callus. 

5. The Hypopleural Row: A row of bristles running in a more or less 
vertical direction on the hypopleura (usually directly below the posterior 
spiracle or above the hind coxa). The bristles may be grouped in a tuft. 

6. The Intra-alars: A row of two or three bristles just laterad of the posterior 
dorsocentrals. 

7. The Mesopleural Row: A prominent row of bristles in front of the meso- 
pleural suture and below the dorsopleural suture. 

8. The Notopleurah: Usually two bristles inserted directly above the dorso- 
pleural suture, between the humeral callus and the root of the wing. 

9. Post-alar s: Bristles on the post-alar callus directly back of the supra-alar 
row and the intra-alars. 

w. Post-humerals: Two or three bristles located just behind the humeral 
callus on the mesonotum. 

//. Prescutellar Row: A name applied to the row of bristles just in front 
of the scutellum and consisting of the caudal dorsocentrals and acrostichals. 

12. Presuturals: One or more bristles just in front of the outer end of the 
transverse suture and above the presutural depression. 

/j. The Sternopleurals: One or several bristles on the sternopleura and 
directly below the Sternopleural suture. These are often arranged two in 



THE DIPTERA: FLIES 



225 




Fig. 85. The principal external structures of the thorax of the blowfly, 
Calliphora viridesccns, and the arrangement of the macrochaetae. (After 
Walton.) 

front and one behind (written "sternopleurals 2:1"); one in front and two 
behind (1:2); two in front and two behind (2:2) ; etc. 

14. The Sub-lateral Row: Frequently the anterior posthumerals and the 
inner presutural are treated as a row and bear the above name. 



226 MEDICAL ENTOMOLOGY 

15. The Supra-alar Row: Usually one to four bristles in a row above the 
root of the wing between the notopleurals and the post-alars. 

CLASSIFICATION OF THE DIPTERA 

The Diptera are divided into two suborders, the Orthorrhapha or the 
straight-seamed flies and the Cyclorrhapha or the circular-seamed flies. 

The Orthorrhapha includes those flies in which the pupa escapes from the 
last larval skin through a transverse or T-shaped slit near the anterior end, 
or by a transverse slit between the seventh and eighth abdominal segments. 
The larva usually has a well-developed or somewhat reduced head. The 




*s 



Fig. 86. Wing of Calliphora viridcscens (= C. lividd) with veins and cells labeled. 
(After Walton, Entomological News.) 

pupa is naked, never enclosed in the last larval skin. The adults are either 
slender flies with long and many-jointed antennae or robust flies with re- 
duced antennae. The venation of the wing is simple (Figs. 56,57) . 

The Cyclorrhapha include those flies in which the pupa is not naked but 
is enclosed in the last larval skin the puparium. The adult emerges through 
a round opening made by pushing of! a cap at the anterior end by means of 
the ptilinum. The adults possess a frontal lunule that is delimited by the 
frontal suture (Fig. 84). The wing venation is more complicated (Fig. 86). 

SUBORDER ORTHORRHAPHA 

This suborder is divided into two series that are difficult to differentiate 
as there are no well-defined and clear-cut separating characters. 



THE DIPTERA: FLIES 227 

SERIES I, NEMOCERA (Nematocera) : In this series the larva possesses 
a well-developed head with mandibulate mouth parts; the pupa is free, not 
enclosed in the last larval skin. The adults have long antennae, many-jointed 
(8 to 1 6 or more), usually longer than the head and thorax, and the joints 
nearly similar; the palpi are pendulous, consisting of one to five segments. 
The anal cell (ist A) is not narrowed toward the margin of the wing and 
the discal cell is generally absent (Fig. 86) . 

The Ncmocera include some twelve or more families of flies. Only four 
of these families contain species known to be of medical importance; in two 
of these families only a small group of species is of significance. 

SERIES II, BRACHYCERA: In this series the larval head is usually re- 
duced, generally retractile, the mandibles acting vertically instead of 
horizontally; the pupa is free. The antennae are shorter than the head and 
thorax, generally three-jointed; the last segment is elongate and often an- 
nulate; style or arista, when present, is terminal, palpi are porrect, one- or 
two-jointed. Discal cell usually present and the anal cell is closed or narrowed 
before the margin of the wing (Figs. 56,57) . 

THE SUBORDER CYCLORRHAPHA 

This suborder includes a large number of families. Their classification is 
in a very unsatisfactory condition since well-defined differentiating characters 
have not been found. At present the suborder is divided into two series, the 
Aschiza and the Schizophora. 

SERIES I, THE ASCHIZA: In this series the adults do not possess a 
frontal suture, or it is restricted; the ptilinum is nonpersistent, not being 
retained after the adult emerges from the puparium. The series contains 
four families of which one, the Syrphidae or hover flies, is of medical im- 
portance (see pp. 524-527). 

SERIES II, THE SCHIZOPHORA: The adults possess a frontal suture, 
well marked, and the ptilinum persists as a structure retained within the 
head, directly behind the suture. This series is composed of a large number 
of families, many of them of the greatest interest to the medical entomologist. 
It is generally divided into two sections, the Myodaria and the Pupipara. 

Section I, Myodaria: The Myodaria or muscoidean flies is the largest group 
of Diptera, including many families and probably more than half of all the 
living species of flies. This section is further divided into two subsections, 
the Acalypteratae and the Calypteratae. 

In the Acalypteratae the squamae or calypteres are small or vestigial and 



228 MEDICAL ENTOMOLOGY 

do not conceal the halteres; the transverse suture of the thorax is usually 
not distinct. This group contains many families of small, to very small, flies; 
a few are of importance to man and are discussed on pages 527-528. 

In the Calypteratae the squamae or calypteres are well developed, large, and 
frequently conceal the halteres; the transverse suture of the thorax is distinct 
and prominent. The flies are moderate to large in size. Here belong the house- 
flies, flesh flies, blowflies, etc. 

Section II, Pupipara: The Pupipara is a remarkable groUp of flies. They are 
all, except Braula, bloodsucking ectoparasites of mammals and birds. Their 
structure has been greatly modified to fit them for their parasitic habits. 
Their bodies are tough, leathery, and the abdomen is indistinctly segmented; 
they may be winged or wingless and the mouth parts are fitted for piercing 
and sucking blood. Larval development takes place within a uterinelike 
structure of the female (except Braula), and the young are deposited as 
full-grown larvae. Some of the species are of importance as they attack 
domestic and game animals and act as vectors of disease (the sheep tick or 
ked, Melophagus ovinus and Trypanosoma melophagium, the causative agent 
of sheep trypanosomiasis; Lynchia maura and Haemoproteus columbae of 
pigeons). 

It is not feasible to prepare a key to all the families of Diptera that affect 
man. The following table will aid in separating the more important families 
of Diptera that are of medical importance: 

KEY TO THE PRINCIPAL FAMILIES OF DIPTERA (ADULTS) 

ASSOCIATED WITH HUMAN DISEASE OR KNOWN 

AS BLOOD SUCKERS 

1. Flies of a leathery or horny texture, living in the adult stage as blood- 

sucking ectoparasites on birds or mammals; they may be winged, 
wingless, or with vestigial wings; abdomen not distinctly divided 
into segments; the antennae are short and inserted in small pits, not 

easily seen. (The group Pupipara) 2 

Flies not as described above: abdomen with distinct segments; never 
external parasites living as adults on birds or mammals; antennae not 
inserted in pits, usually easily seen; usually with one pair of wings 4 

2. Head small, narrow, folded back in a groove in the thorax. Wingless. 

Parasites of bats Nycteribiidae 

Head not as described above, in normal position 3 

3. Palpi elongate, forming a sheath for the piercing mouth parts. Usually 



THE DIPTERA: FLIES 229 

winged with the veins crowded anteriorly. Parasites of birds and 

mammals Hippoboscidae 

Palpi not forming a distinct sheath for the piercing mouth parts but 
broad and leaflike. Winged or wingless and in the winged forms the 
veins evenly distributed. Parasites of bats Streblidac 

4. Antenna consisting of eight or more freely movable, nearly similar 

segments; anal cell (Fig. 93) widens toward the margin of the wing. 

The group Nemocera 5 

Antenna consisting of not more than four or five well-defined segments; 
the segment beyond the second may appear as more or less consoli- 
dated into rings or annuli 9 

5. The costal vein is not continued beyond the apex of the wings; hairs 

and scales seldom present (Fig. 145) 6 

The costal vein surrounds the wing; hairs, often dense, on the wing or 
scales present on the veins, especially on costa and posterior margins 
of wing 8 

6. Antenna shorter than the thorax, composed of ten or eleven closely 

united, similar segments; never plumose; legs strong, the hind pair 
more or less dilated: body thickset; wings broad with few veins. 

(Black flies) Simuliidae 

Antenna longer than the thorax, usually bushy with long hairs. In 
general not as described above 7 

7. Dorsum of thorax with a longitudinal groove; wings narrow and, in 

life, held more or less roof like; mouth parts not fitted for piercing. 

(None are known to be of medical importance; the gnats) 

Chironomidae 

Dorsum of thorax without a longitudinal groove; wings held flat and 
superimposed over each other when at rest; wings often spotted 

(Fig. 153). Mouth parts fitted for piercing. (Punkies) 

(Heleidae) Ceratopogonidae 

8. Small mothlike flies; mouth parts very short; wings and body clothed 

with long hairs; wings with long parallel veins; scales on wings ab- 
sent Psychodidae 

A. Wings with the second longitudinal vein three-branched, the 

third branch arising near the base. (Fig. 88). Not known 

to be of medical importance Subfamily Psychodinae 

AA. Wings with the second longitudinal vein three-branched, the 

third branch arising near the middle of wing (Fig. 88). 

(Of great medical importance) . . . Subfamily Phlebotominac 



230 MEDICAL ENTOMOLOGY 

Not mothlike flies; posterior margin of wings and most of the veins 

with coarse scales (Fig. 93); mouth parts elongate, slender, well 

adapted for piercing (most species) . (The mosquitoes) .... Culicidae 

9. Antenna consisting of four or five segments, the segment beyond the 

second may appear as more or less consolidated into rings but can 

be easily counted (3 to 8 rings) ; squamae large. (Horseflies) 

Tabanidae 

Antenna consisting of only three segments 10 

10. Last segment of antenna small and ending in an elongate style or 

arista (Fig. 162) . (The snipe flies) Rhagionidae 

Last segment much larger than the others and with a dorsal arista 
either bare or plumose (Fig. 51 /) or a terminal arista n 

11. Wing with stout veins (2 or 3) near the inner costal border; other 

veins are weak and extend outward to the wing margin; no cross 

veins Phoridac 

Wing not as described above 12 

12. Anal cell elongate reaching nearly to the margin of the wing; a spurious 

or false vein present between the third and fourth longitudinal veins; 

usually brightly colored, flower-loving flies (F"ig. 211) Syrphidae 

Anal cell short, truncate (Fig. 172 a) ; spurious vein absent 13 

13. Second antenna! segment with a longitudinal cleft or suture on its up- 

per outer edge (Fig. 51 ds); squamae usually conspicuous; thorax 

generally with a conspicuous transverse suture 14 

Second antennal segment without a longitudinal cleft on its upper, 
outer edge; squamae usually small or very small; thorax usually with- 
out a complete transverse suture 18 

14. Mouth parts vestigial. (The warble flies and botflies, including Cutere- 

bridae and Hypodermatidae) Oestridac 

Mouth parts well developed and functional 15 

15. Hypopleura without a well developed row of bristles below the pos- 

terior spiracle (Fig. 85). Small hairs may be present. Arista of antenna 
usually hairy or plumose. (Houseflies, stable flies, glossina flies) .... 

Muscidae (and Anthomyiidae) 

Hypopleura with a well-developed row of bristles (Fig. 85) or tuft 
of bristles 16 

16. Postscutellum and postnotum appearing in side view as double con- 

vexities (double chin effect under the scutellum). Usually strongly 

bristled flies. All parasites as larvae, mostly on other insects 

Tachinidae 



THE DIPTERA: FLIES 231 

Postscutellum not strongly developed so that only the single convex 
postnotum appears in side view 17 

17. Flies in which the coloration is largely metallic, blues, dark blues, black, 

or shades of green. A few species are not metallic but have golden 
hairs on the thorax among the bristles (Pollenia)\ usually four 

notopleural bristles present. (The blowflies) Calliphoridae 1 

Flies in which coloration is mainly gray, silvery, intermixed with darker 
colors; rarely more than two notopleural bristles present. (The flesh 
fli es ) Sarcophagidae 1 

18. Mouth parts vestigial, sunk in a tiny oval pit; large, brownish, fuzzy 

flies (15 mm. or more). (Horse botflies; Figs. 206-208) Gasterophilidae 
Mouth parts well developed, not sunk in a pit 19 

19. Subcosta vestigial; if present it extends but a short distance beyond 

the humeral cross vein but does not reach the costa 20 

Subcosta present and extending to the costa (but must be looked for 
with care as it is almost concealed beneath the base of the ist longi- 
tudinal 21 

20. Sixth longitudinal and anal veins absent; ocellar triangle large as 

compared with size of head; subcosta only present at base and ap- 
pears as a minute fold; costa with only one fracture (Fig. 178). Very 

small flics (i to 3 mm.). (Eye gnats) Chloropidae 

Sixth longitudinal vein and usually anal vein present; subcosta more 
distinct but docs not reach the costa; costa with two fractures. (The 
fruit flies) . Drosophilidae 

21. Palpi vestigial. Small, shiny black, brown, or reddish flies with few 

bristles. Head spherical and abdomen wasp-shaped Sepsidae 

Palpi well developed. Also small flics but not of the shape indicated 
above. (The cheese skipper) Piophilidae 

A KEY TO THE LARVAE OF SOME OF THE FAMILIES OF 
DIPTERA MENTIONED IN THE KEY TO THE ADULTS 

i. Head well developed, enclosed in a horny capsule, not retractile; mouth 

parts normal, the mandibles moving laterally in feeding 2 

Head not well developed but if partially developed the mandibles move 
vertically, parallel to each other or obliquely inward; or with no visible 

1 These two family names are retained here though the grouping of the genera of 
the Musciclac, Calliphoridae, and Sarcophagidae varies with different specialists. These 
, names are still in common usage in medical literature and include the most important 
genera affecting man and animals. 



232 MEDICAL ENTOMOLOGY 

head, and the anterior end pointed and provided with mouth hooks 
or reduced parts (Figs. 159,160,173); or the entire larva grublike, 
rounded at both ends (Fig. 210) ; or, possessing an elongated siphon at 
end o abdomen (Fig. 211) 7 

2. Aquatic or semiaquatic larvae, living only in swift streams or in tree- 

holes, mud, edges of ponds, or in open water 3 

3. Prolegs lacking on all segments of the body 4 

Prolegs present on some segments of the body (Fig. 149) 6 

4. Head distinct; thorax and abdominal segments divided secondarily into 

annuli or rings, usually each ring with a dorsal plate; respiratory 

openings on prothorax and anal segments (amphipneustic) 

Psychodinae 

Head distinct; the segments of thorax and abdomen without secondary 
divisions and otherwise differing from above couplet 5 

5. Thoracic segments fused, forming a more or less greatly enlarged portion, 

distinctly thicker than the abdomen (Fig. 105) ; respiration by spiracles 
located at end of elongated tube (siphon) or flattened posterior spiracles 

(metapneustic). (Mosquitoes, see pp. 250-332) Culicidae 

Thoracic and abdominal segments about equal in diameter, the thoracic 
segments not greatly enlarged; larvae snakelike (Fig. 152 C) with 

rather smooth bodies. (Culicoides, Bezzia, and others; punkies) 

(Heleidae) Ceratopogonidae 

6. Two prolegs on each of abdominal segments i and 2; tracheae ending in 

a pair of discs on eighth abdominal segment Dixidae 

Prolegs (usually only a single one) confined to the prothoracic segment; 

posterior end of larva with an adhesive disc for attachment. (Larvae 

confined to more or less swift water; black flics) Simuliidae 

Prolegs present on prothorax and posterior end of body or they may be 

reduced; never as above. (Gnats) (Tendipcdidae) Chironomidae 

Larva with well-developed head and provided with stout bristly hairs or 
spines (Fig. 90 b) ; body with similar hairs; tip of abdomen with two 

groups of long hairs; abdomen with prolegs. (Sand flies) 

Phlebotominae 

7. Larvae cylindrical pointed at both ends; mandibles present, hooklike, and 

move vertically, parallel to each other; respiratory organs (spiracles) 
located in a vertical cleft, and usually on the tip of a posterior siphon 

(Fig. 160) Tabanidae 

Larvae not as described above 8 

8. Stout, grublike larvae (aquatic) with a long telescopic terminal siphon. 



THE DIPTERA: FLIES 233 

(Rat-tailed maggots; Fig. 211) (in part) Syrphidae 

Larvae not as described above. For identification of larvae which do not 
agree with any of the above descriptions, consult the key given on 
pages 531-533- 

REFERENCES 

Aldrich, J. M. A catalogue of North American Diptera. Smithsonian Misc. 
Colls. 46, Washington, 1905. 

Curran, C. H. The families and genera of North American Diptera. New York, 
1934. (A valuable book.) 

Fauna of British India. The Diptera. London, 1912-1940. 5 vols. (Ex- 
tremely valuable for workers in the East.) 

Lindner, Erwin (editor). Die Fliegen der palaearktischen Region. Stuttgart, 
1925-1935. (A series of volumes; various parts have been published.) 

Walton, W. R. An illustrated glossary of chaetotaxy and anatomical terms used 
in describing Diptera. Ent. News, 20: 307-319, 1909. 

Williston, S. W. Manual of North American Diptera. New Haven, Conn., 
1908. 



CHAPTER IX 



The Psychodidae: 

The Moth Flies, Owlet Midges, 

and Sand Flies 



THE members of this family are long-legged, small mothlike flies rarely 
exceeding 5 mm. in length (Fig. 87). Their bodies and wings are 
densely clothed with hairs. The wings (Fig. 88) are either oval or lanceolate 
in shape and, when at rest, are held rooflike or in an arched manner over the 




Fig. 8j. A sand fly, Phlebotomus vcrruciinim 
Hertig.) 



. (From a photograph presented by 



abdomen. The venation is simple, consisting mainly of longitudinal veins. 
The mouth parts are short and not well adapted for piercing (subfamily 
Psychodinae) or rather long and fitted for bloodsucking (Fig. 89), the 



THE PSYCHODIDAE 235 

subfamily Phlebotominae. The antennae are long, slender, and consist of 12 
to 16 segments, each usually with short hairs. The two subfamilies, Psychod- 
inae and Phlebotominae, may be readily separated by the characters given 
in the key (pp. 228-231). 

The majority of known species belong in the subfamily Psychodinae in 
which the mouth parts are not adapted for bloodsucking. The adults are 
usually whitish, small, mothlike, and are commonly found about kitchens 
and outhouses, along creeks filled with decaying wastes, and about sewage 
disposal plants where they may breed in vast numbers and the adults be 
very annoying. The larvae occur in decaying vegetable wastes, sewage, dung, 
exuding sap on trees, fouled streams, and similar situations. None of the 
species are known to be of medical importance, though their abundance may 
be annoying at times. 




Fig. 88. Left: The wing of a Phlcbotomus sp. Right: The wing of a Psychoda sp. The 
veins and margins of wings are clothed with long hairs but these are omitted, av, 
auxiliary or subcostal vein. The numbers indicate the longitudinal veins. 

* In the subfamily Phlebotominac the adults (usually called sandflies) are 
bloodsucking, the mouth parts being well adapted for piercing (Fig. 89). 
This group contains but a single genus, Phlebotomtts, which has been divided 
into a number of not well defined subgenera. In recent years this family has 
been studied rather intensively, especially in those areas where pappataci 
fever, kala azar, leishmaniasis, and Oroya fever occur. Larrouse (1921) re- 
corded 5 species from Europe, 7 from Africa, 7 from Asia, and 12 from the 
Americas. Sinton (1928) listed 28 species from Asia, and Dyar (1929) re- 
ported 21 species from the Americas, only one being found in North America. 
Barretto (1947) lists over 150 species from the Americas, 6 of which are 
from North America. Adler (1946) reports 10 species from the island of 
Cyprus alone. Kirk and Lewis (1946) report 44 species from the Ethiopian 
region. Yao and Wu (1941) list 13 species from China; Theodor (1948) re- 
ports 127 species and 34 varieties from the Old World. 

DISTRIBUTION: Phlebotomus flies arc widely distributed throughout 
the subtropical and tropical regions of the world. They do not occur very 



236 



MEDICAL ENTOMOLOGY 



far within the temperate zones, being confined between 40 South and 40 
North latitude in the Americas. In Europe and Asia they occur to about 45 
North latitude but their southern limit is not known. They are not known 
to occur in tropical mountain areas above 8000 feet (P. verrucamm in Peru) . 
Though widely distributed, the species are usually restricted to more or less 
definite regions that provide breeding grounds and adequate sources for 
blood. Their flight range is very limited, scarcely exceeding 100 to 200 yards 
from their breeding grounds. 




Fig. 89. Mouth parts of Phlcbotomus sergenti (somewhat diagrammatic). 
Ant, antennae; CI, clypeus; E, eye; Hphy, hypopharynx showing the salivary 
gutter extending throughout its length; Lb, labium; LbEp, labrum-epipharynx; 
M, mandible; MX, maxilla; MxPlp, maxillary palpus. 

BIONOMICS: The biology, under experimental conditions, of a con- 
siderable number of American species (over 25) has been reported during 
the past ten years. Unfortunately not a single American species has been 
found breeding under natural conditions though the habitats and activities 
of the adults of a number of species seem to be well known. The larval 
habitats of several European and Asiatic species have been discovered in 
certain areas, but many details of their activities are still lacking. Phlcbotomus 
papatasii Scopoli (Fig. 90), the vector of three-day fever or pappataci fever, 
has been studied extensively in the Mediterranean region and in India. This 
species is the important vector of pappataci fever throughout its range. It 
occurs around the Mediterranean region and along the North African area 
south to the Anglo-Egyptian Sudan east through the former Italian Somali- 
land to Calcutta and north into Central Asia. The adults are partial to hu- 



THE PSYCHODIDAE 237 

man blood and invade buildings, attacking during the evening and at night. 
Their bites are severe and the later irritation is almost intolerable to susceptible 
persons. They are not capable of long flights only a few yards (50 or more) 
but they have been taken in barracks over 25 feet from the ground, and 
Anderson (1939) reports more cases of fever among soldiers in Peshawar 
occupying the second story than those on the ground floor. He reports taking 
the adults 70 feet above the ground level. During the day they hide in holes 
and cracks of walls, crevices, tree holes, dark rooms, latrines, and any place 
of darkness and freedom from air currents. The adult life is believed to be 
comparatively short, probably not over two to three weeks. Under experi- 




Fig. 90. Phlebotomus papatasii Scop, (a) Larva, first instar. () Sketch of adult larva. 
(c) Pupa with larval skin attached, (d) Adult female, resting position. (After Byam and 
Archibald, The Practice of Medicine in the Tropics; from Nevvstead.) 

mental conditions the species is easily reared when the necessary larval food, 
such as moist soil with adequate decaying animal and plant wastes, is pro- 
vided. The females require blood meals for the development of the eggs. 
After the flies mate eggs are laid in small batches, preferably in cracks and 
crevices of the soil. Several batches are usually laid and blood meals are 
required between each batch. Anderson (1939) reared this species in 31 days 
at Peshawar, India, where the temperature ranged from 80 to 84 F. at night 
to 100 to 107 F. during the day. He fed the larvae on desiccated rabbit feces 
and earth. During cool weather the larval life is much prolonged, to 60 days 
or more. Whittingham and Rook (1923) reared this species in Malta from 
egg to adult in 42 days. There are four larval stages, and hibernation takes 
place in the fourth larval stage. The main larval habitats were in loose soil, 
cracks of buildings, embankments, but not in wet soil. Recently Uns worth and 



238 MEDICAL ENTOMOLOGY 

Gordon (1946) succeeded in establishing and maintaining a colony for ex- 
perimental work at the University of Liverpool. 

Phlebotomus argentipes has been studied in the region of Calcutta, India^ 
It is one of the important vectors of kala azar. Smith et al. (1936) report its 
primary breeding grounds as in the soil within a range of 20 yards of dwellings, 
cattle sheds, and similar places where there is vegetation and contamination 
of the ground. The larvae were found mostly in the first three or four inches 
and localization was frequent. Though this species seems to prefer cattle 
blood, yet it will attack humans. It is widespread in India east and south of 
a line drawn from Simla to Bombay (Sinton, 1932). It also occurs in Burma. 

Phlebotomus sergenti is widely distributed in the Near and Middle East, 
in North Africa, Mesopotamia, Iran, and northwest India. It is an important 
vector of Oriental sore. 

In North America six species of Phlebotomus are now known. Only one 
species, P. diabollcus Hall, is known to bite man. Very little is known of its 
biology, though it has been reared in captivity and its life cycle requires 28 
to 50 days. The species is known only from southwestern Texas. Its breeding 
grounds have not been discovered. No species of Phlebotomus have been 
found north of line from Washington, D.C., to San Francisco. 

In Mexico and Central America 9 species are listed by Barretto (1946), 
while in South America over 136 species are recognized by the same author 
(1947). These species are widely distributed over South America south to 
Buenos Aires and east of a line drawn from Lima, Peru, to Buenos Aires. 
No species are recorded from Chile. Only a few of the species can be men- 
tioned here. 

Phlebotomus intermedius Lutz and Neiva ( = lutzi), a vector of muco- 
cutaneous leishmaniasis and of kala azar (experimental), is widely distributed 
in South America from Venezuela to Argentina, though most records are 
from Brazil, Paraguay, and Argentina. Bayma (1936), Chagas (1938) and 
Barretto (1940) have reared this species under experimental conditions. The 
eggs were obtained from captured females and the larvae reared in earth 
(rich) usually supplied with animal or decomposing vegetable matter under 
proper moisture and temperature conditions. At the optimum temperature 
of 26 to 27 C. the life cycle from egg to adult required 36 days; if the tem- 
peratures were lowered to 20 to 22 C. it required 52 or more days. Unfortu- 
nately nothing seems to be known about their natural breeding places. The 
adults are crepuscular and nocturnal in their feeding habits. They are more 
or less domestic in their habits and readily enter buildings for human or 
other animal blood. 



THE PSYCHODIDAE 239 

Phlebotomus verrucarum Townsend is the well-known vector of Oroya 
fever or verruga peruana. It occurs only in the high mountain canyons in 
Peru (between 6 and 13 South latitude) especially in the Rimac and Santa 
Eulalia Valleys at elevations of 800 to nearly 3000 meters. Its distribution out- 
side these valleys is not well known. The adults occur abundantly in certain 
areas in these valleys, especially in houses and less abundantly in caves, crev- 
ices, or other outdoor situations. Though it has been reared many times under 
experimental conditions, its natural breeding grounds seem to have escaped 
the most diligent search. The life cycle at temperatures of 23 to 25 C. is 
completed in 6 to 8 or more weeks. Breeding continues throughout the year, 
though in cold weather hibernation takes place in the last larval stage (4th 
instar). The adults are constant invaders of human habitations and prefer 
human blood, feeding primarily during the evening hours and at night. They 
also feed on dogs, monkeys, donkeys, and the larger mammals. The other 
two species usually associated with P. verrucarum in these high canyons and 
valleys are P. noguchli Shannon and P. pentensis Shannon. According to 
Hertig (1942), P. nogtichii rarely enters houses, does not feed on man, and 
its only known hosts arc field mice; P. pentensis occurs in caves but also enters 
houses and feeds on dogs and man. 

With the more or less definite proof (confirmed in 1940) that the various 
human Icishmania diseases are transmitted by species of Phlebotomus, the 
study of these insects received great impetus in South America where muco- 
cutancous and cutaneous leishmaniases (caused by Leishmania braziliensis 
and L. tropica) are widely distributed; the more recent discovery of kala azar 
in Brazil by Chagas (1936) added greatly to the necessity for these studies. 
The work of Barretto (1940 to 1947) and others led to the recognition of 112 
new species in South America since 1936, out of a total of 136 species. In 
addition, the biology, at least under experimental conditions, of nearly 20 
species has been reported when previously only three or four species had been 
reared. Experimental work on the transmission of these diseases by various 
species of Phlebotomus has greatly increased. At present six species have been 
incriminated as vectors of Leishmania braziliensis experimentally or have 
been found naturally infected; at least two species have been shown capable 
of transmitting kala azar under experimental conditions. The importance 
of Phlebotomus species as transmitters of disease is well recognized; this is 
particularly true in Central and South America and in Mexico. 

Unfortunately the study of the species of Phlebotomus is so difficult that 
only specialists in the group are qualified to make identifications of the adults. 
These are based on the structures of the male genitalia (Fig. 91), of the 



240 



MEDICAL ENTOMOLOGY 



spermatheca of the females, of the hypopharynx, and of other minute charac- 
ters. The larvae are distinctive (Fig. 90) hut no one has ventured to offer 
keys to separate even the species that have been reared. 



DC 



DC 




Io 



Fig. p/. Male gcnitalia of Phlcbotomus vcrrucarum. DC, dorsal clasper; Dsp, 
dorsal side piece; la, intermediate appendage; Io, intromiltent organ; Vc, ventral 
clasper. 

PHLEBOTOMUS AND DISEASE 

PAPPATACI FEVER, THREE-DAY FEVER, OR SAND-FLY 
FEVER: This disease is endemic throughout the Mediterranean region, India, 
Ceylon, parts of China, East Africa, and parts of South America. The disease 
is characterized by sudden onset, fever of 103 to 104 F., which usually falls 
on the third day, severe headache, and pains. Recovery is usually slow bur 



THE PSYCHODIDAE 241 

mortality is nil. The etiological agent is a virus that has not been isolated. 
It is present in the blood stream 24 hours before the onset o the disease and 
disappears in from 24 to 48 hours of the disease. Doerr and his associates 
(1908, 1909) demonstrated that P. papatasii could transmit the virus of this 
disease, and their work has been confirmed by numerous investigators. The 
fly obtains the virus during its presence in the blood stream of patients suf- 
fering from the disease. In the fly there is an incubation period of six to nine 
days before the fly is capable of transmitting the virus. The incubation period 
in man is from three to ten days. Whittingham and Rook (1923) demon- 
strated that infected sand-flies can transmit the virus to their offspring, and 
Moshkovsky (1937) obtained similar results. Sabin et aL (1944) were unable 
to confirm these results. Though this disease is present in regions where 
P. papatasii is not known to occur, yet no other vector has been discovered or 
incriminated up to the present time. There is no known animal reservoir 
except man. 

OROYA FEVER, VERRUCA PERUANA, OR CARRION'S DISEASE: 
Oroya fever and verruga peruana were long regarded as distinct diseases, or 
different manifestations of the same disease as held by Peruvian physicians. 
Oroya fever is the severe form of the disease and is characterized by 
high fever and anemia, often resulting in death. Verruga peruana is the 
cutaneous form involving verrucous eruptions or nodules, with usually few 
deaths. The former has been called "Carrion's disease" after Daniel Carrion, 
a student at Lima, who, on August 27, 1885, infected himself with blood from 
a verruga nodule and developed Oroya fever from which he died, thus 
apparently proving that the two diseases were in some manner connected. 
The disease is restricted to high, narrow, mountainous valleys, principally 
on the western slopes of the Andes in Peru between 6 and 13 South latitude. 
It has recently been reported from southern Colombia, Ecuador, and the 
eastern slopes of the Andes, thus extending the known distribution to 2 North 
latitude. The disease appears to be restricted to elevations of from 2500 to 
about 8000 feet in these areas. Practically all persons living in the zones of 
the disease suffer from the disease and become immune. However, it is very 
deadly to nonimmunes as demonstrated during 1870 when over 7000 persons 
died while trying to build a railway from Lima to Oroya. Later epidemics 
occurred during the construction of bridges and tunnels. 

The etiological agent is Bartonella bacillijormis Strong et al. (1915). This 
organism occurs in the red blood cells and the reticulo-endothelial cells of 
the lymphatic system and the viscera. It has been successfully cultured, and 
infections have been produced in monkeys with these cultures, though ap- 



242 MEDICAL ENTOMOLOGY 

parently only the verruga type; no case of Oroya fever has been produced 

in monkeys. 

TRANSMISSION: Townsend (1913, 1914) was the first to incriminate Phle- 
botomus flies as the vectors and he described P. verrucafiim as the transmitter 
in the high valleys of PcruJHis experiments, though not absolutely conclu- 
sive, demonstrated that his assistant (out of three sleeping in the verruga 
area) came down with the disease after being bitten by sand flies (55 bites) 
through accidental exposure of his arms while sleepfng under a net. The 
other two were not bitten. A second case was of a British sailor who permitted 
himself to be bitten by wild sand flies and who developed what appeared to 
be the disease, but confirmation of this was apparently never established. 
"It is most unfortunate that this experiment should have resulted incon- 
clusively for lack of definite diagnosis of the subject's various clinical symptoms, 
since it is the only recorded human transmission experiment with Phleboto- 
mus" (Hertig, 1942). Townsend's work was not confirmed till Noguchi and 
his associates (1929) succeeded in transmitting the disease to monkeys by 
crushed, infected Phlebotomus verrucarum sent from Peru to New York by 
Shannon. Though much experimental work has been done on the trans- 
mission of this disease, the results are not very gratifying. Battistini (1929, 
1931) succeeded in infecting monkeys both from the bites of wild flies and 
from the injection of suspensions. Hertig (1942) succeeded in infecting five 
out of eight monkeys by the bites of wild sand flies taken in the verruga zone 
in Peru. He also succeeded by using inoculations of cultures of Bartonella 
bacilltjormls. In no case did he observe a typical case of Oroya fever but he 
did demonstrate the presence of the etiological agent in the experimental 
animals. Hertig's (1042) work has apparently proved that only P. verrucarum 
is the vector in the Peru area as P. noguchii does not bite humans and rarely 
enters houses; P. peruensis is usually scarce and is restricted to the upper part 
of the zone of verruga disease in the Rimac and Eulalia Valleys. Hertig 
(1942) was unable to find any developmental cycle of the etiological agent 
in the sand flies, though he found massive infections of the proboscides of both 
males and females, taken in the wild, with organisms not quite typical of 
B. bacilli formis. What relation these massive infections have in relation to 
verruga is still undetermined. At the present time only P. verrucarum has been 
definitely incriminated as a vector, yet no direct human infection by the bites 
of this species has been made. As the disease has been found in areas in 
Colombia and Ecuador, other species of Phlebotomus must be involved. 
There is no known animal reservoir except man. 

As there is no known treatment for either Oroya fever or the verruga 



THE PSYCHODIDAE 243 

stage, it would seem that the use of DDT might prove effective in destroying 
the adults either by direct spraying or by residual effects. Some of the new 
repellents might also prove efficient. As their breeding grounds have never 
been found, nothing can be done in the control of larvae. 

KALA AZAR OR VISCERAL LEISHMANIASIS: "Kala-azar is an 
acute, sub-acute or chronic infectious disease caused by a protozoan parasite, 
Leishmania donovani Ross, 1903 or L. injantum Nicolle, 1908, occurring in 
children and adults, and characterized by splenic and hepatic enlargements, 
an irregular remittent fever, progressive anaemia, leucopenia, cachexia, and a 
high mortality" (Archibald, 1921). This disease has a wide distribution 
around the Mediterranean, is local in the Sudan, Transcaucasia, Turkestan, 
Kenya, French Equatorial Africa, and Nigeria, and covers an extensive area 
in northeast India and in China from Canton north to Peking, extending 
deep into Manchuria with many scattered areas in other parts of China. 
Recently (1936 and later) it has been found in northeastern Brazil, and the 
Chaco region of the Argentine, with scattered reports of cases in various 
other parts of South America. Before the development of the newer treat- 
ments with various antimony compounds (1915) the death rate was about 
95 per cent of cases (Napier, 1946). Still newer and better treatments have 
been developed so that the disease is not the terror it was in the days when 
vast numbers died in epidemic waves, such as swept through Bengal, Assam, 
and other parts of India. After the discovery of the causal organism intense 
search followed to determine the method of transmission. It can only be 
transmitted from the sick to the well by some stage of the parasite Leishmania 
donovani, and this would require some vector as all other means of transmis- 
sion had been negative. Phlebototmts flies were early suspected (Sergents, 
1904) as vectors of leishmania and certain species when fed on the blood of 
kala azar patients showed the same development stages in their intestines 
as in artificial cultures the leptomonad stage. Yet despite the development 
of this flagellate stage and its migration forward to the esophagus, pharynx, 
and buccal cavity of the experimental flies, all efforts to obtain infection in 
experimental animals or human volunteers proved failures. However, Shortt 
ct al. (1931), Napier ct al. (1933), and Smith and Murkirjee (1936) reported 
successful infections of hamsters by the bites of infected P. argentipes. These 
consisted of only three apparently successful transmissions out of a large num- 
ber of trials. Though numerous experiments were carried out with these flies, 
it was not till Smith ct al. (1940) recognized the significance of what are now 
called "blocked" flies that rapid progress was made in solving the relation 
of Phlebotomus flies to kala azar transmission. They discovered that when 



244 MEDICAL ENTOMOLOGY 

flies were fed on infected blood and later fed on plant juices such as that of 
raisins, the anterior end of the intestine, the esophagus, and the pharynx be- 
came so plugged with the developing leptomonad stage that the flies could 
not successfully obtain a blood meal. They would try to feed again and again 
but in so doing liberated great numbers of what may be called the infective 
stage of the parasite into the host. Experiments with "blocked" infected P. 
argentipes by these investigators readily demonstrated the transmission of kala 
azar to mice and hamsters (1940, 1941). Finally Swanimath et at. (1942), 
using the same technique, successfully transmitted kala azar by "blocked" 
infected flies to five human volunteers. All bitten by these flies developed the 
disease within five to eight months. These were the first successful infections 
of man and the transmission problem seems solved for this species of Phle- 
botomus. Whether this may also prove true for other species suspected of 
transmitting leishmania diseases remains to be determined. 

DERMAL LEISHMANIASIS: The form of the disease that occurs most 
commonly about the Mediterranean region is dermal leishmaniasis, though 
the visceral (kala azar) is also present, especially in Greece, Crete, and scat- 
tered in all the area. It is mainly a children's disease here, hence the name of 
the parasite, Leishmania infanturn (this is now considered identical with 
L. donovant). Dogs in this region are heavily infected and serve principally 
as the source of human infection. (Apparently dogs have not been found 
infected in India, though they are known to be infected in North China.) 

VECTORS OF KALA AZAR AND DERMAL LEisHMANiAsis: In India the principal 
vector is Phlebotomus argentipes and the distribution of the disease cor- 
responds closely with the known distribution of the fly. In China the accepted 
vector (though apparently no human infections have been proved by experi- 
mental work) is P. chincnsis and probably P. scrgenti mongolensis; in the 
Mediterranean area it is mainly P. perniciosus, though in Greece P. major is 
the vector (Malmos, 1947) ; in the eastern Mediterranean P. papatasii is in- 
volved, but in North Africa P. sergenti is considered important. In the Sudan 
and other parts of Africa the vectors have not been determined. In South 
America Chagas (1939, 1940) incriminated P. intermedius (= lutzt) and 
P. longipalpis. With the known ease with which these flies can be raised under 
laboratory conditions, it should not be long before experiments with "blocked" 
flies should give adequate data on the principal vectors throughout the world. 

ORIENTAL SORE; ALEPPO, BAGDAD, OR DELHI BOIL; ETC.: 
This is a cutaneous leishmaniasis caused by Leishmania tropica. The disease 
is widespread about the Mediterranean basin; in Africa south to Angola on 



THE PSYCHODIDAE 245 

the west and to the Sudan and Abyssinia on the east; in Arabia, Mesopotamia, 

Iran, southern Russia, India, China; and throughout southern Mexico, Cen- 

tral America, and all of South America except Chile. The disease is restricted 

to the skin, forming ulcers, and a single infection is said to confer immunity. 

Transmission may be by direct contact with the ulcers. In some countries 

children are inoculated in those parts of the body where the healed scar will 

not be observed. However the main agents 

in the transmission of L. tropica are Phle- 

botomus flies. Adler and Ber (1941) re- 

port successful transmission of L. tropica 

by P. papatasii in Palestine. They obtained 

28 lesions from the bites of 26 infected sand 

flies. In India P. papatasii and P. sergenti 

are considered the vectors; in Italy P. 

macedonicum is reported as a vector; in 

North Africa P. sergenti probably is the 

vector; in the Americas no definite species 

have been incriminated. 

Mucocutaneous leishmaniasis or espun- 
dia is an ulcerating infection of the skin 

that may also involve the margins of the F 'S> 9^ Photograph of worker with 
, , f , IT- Leishmania lesion developing in ear. 

nose and the mucosa of the mouth. It is 




(Arfow ^^ o 

caused by Leishmania brasihensis. The 
disease is widespread in South and Central America and as far north as 
Yucatan. In many rural areas as in Minas Geraes in Brazil and in Yucatan 
among the chicle workers (Fig. 92) this is a serious disease. The transmitters 
are species oiPhlebotomus and the following have been incriminated in South 
America: P. arthuri (?), P. fischeri (Pessoa and Coutinho, 1941), P. inter- 
medius (Aragao, 1922, 1927), P. migonci (Pessoa and Coutinho, 1941, and 
others), P. pessoai (Pessoa and Coutinho, 1940, 1941), and P. whitmani 
(Pessoa and Coutinho, 1941). 

RESERVOIRS 

In the Mediterranean region dogs are probably the chief reservoir of kala 
azar though cats play a part; dogs are also known to be naturally infected 
in China, but not in India. Experimentally many animals are readily in- 
fected as guinea pigs, rabbits, gerboas, gerbils, hamsters, jackals, dogs, and 
monkeys. The reservoirs of L. tropica and L. brasiliensis are probably man 



246 MEDICAL ENTOMOLOGY 

though certain species of monkeys, dogs, cats, rats, mice, guinea pigs, and 
others can be experimentally infected. 

CONTROL OF SAND FLIES 

So little is known about the breeding grounds of sand flies that it would 
be impossible to indicate any measures that might be of value in reducing 
the abundance of flies. In the case of P. papatasii proper building measures to 
reduce cracks, crevices, etc., in walls might be of some aid. P. sergenti might 
be reduced by avoidance of contaminating the ground about homes with 
animal or vegetable wastes. Nothing is known about the breeding grounds of 
the other species. The adults might be adequately controlled by the proper 
use of DDT sprays in buildings, cracks, crevices, or known places where the 
adults rest during the day. If applied in sufficient quantities the residual 
effect might be lasting. Hertig and Fairchild (1948) demonstrated the effec- 
tiveness of 5 per cent DDT (by weight) in kerosene in Peru during the years 
1945-1947. House spraying and spraying of stone walls, resting caves, shelters 
of all kinds, and suspected breeding areas gave excellent control and the 
residual effect was very lasting (12 to 19 months on stone walls). This treat- 
ment to be most effective should be applied to all buildings, all shelters, stone 
walls, caves, and other places where sand flies rest since the above authors 
found that untreated areas only 75 to 100 yards distant were still swarming 
with the flie.s. This method of control should be very effective for sand flies 
in many parts of the world owing to their resting and flight habits. Further- 
more, their long larval cycle would prevent rapid multiplication and thus 
reduce the number of treatments. In addition to controlling the sand flies, 
other insects as mosquitoes and houseflies would be greatly reduced. 

REFERENCES 

*Addis, C. f. Collection and preservation of sandflies (Phlebotomus) with keys 
to United States species. Trans. Amer. Micr. Soc., 64: 328-332, 1945. 

. Laboratory rearing and life cycle of Phlebotomus (Dampfomyia) antho- 

phoms Addis. Jl. Parasit., 31: 319-322, 1945. 

Adler, S. The sandflies of Cyprus. Bull. Ent. Res., 36: 497-511, 1946. 

, and Ber, M. The transmission of Leishmania tropica by the bite of Phle- 
botomus papatasii. Ind. Jl. Med. Res., 29: 803-809, 1941. 

, and Theodor, O. The transmission of Leishmania tropica from artificially 

infected sandflies to man. Ann. Trop. Med. Parasit., 21 : 89-104, 1927. 

, and Theodor, O. Investigations on Mediterranean kala-azar. Proc. Roy. 

Soc., B., 108: 447-502, 1931. 



THE PSYCHODIDAE 247 

Anderson, W. M. E. Observations on P. papatasii in the Peshawar district. Ind. 

Jl. Med. Res., 27: 537-548, 1939. 

Barretto, M. P. Processes de captura, transports, dissec^ao e montagem de Fle- 
botomos. Anais Fac. Med. Univ., S. Paulo, 16: 173-187, 1940. 
. Morfologia dos ovos, larvas e pupas de alguns Flebotomos de Sao Paulo. 

Mid., 17: 357-427. I94 1 - 
. Observa^oes sobre a biologia, em condi^oes naturals, dos Flebotomos do 

estado de Sao Paulo. Thesis, Univ. da Sao Paulo, 1943. 
. Sobre a sinonimia de Flebotomos americanos. Anais Fac. Med. Univ. S. 

Paulo, 22: 1-27, 1946. 
. Catalogo dos flebotomos americanos. Arq. de Zoologia do Estado de Sao 

Paulo, 5 art., 4: 177-242, 1947. 
Bequaert, J. C. The distribution of Phlcbotomus in Central and South America. 

Carnegie Inst. Wash., Pub. No. 499: 229-235, 1938. 
Berberian, D. A. Successful transmission of cutaneous leishmaniasis by the bites 

of Stomoxys calci trans. Proc. Soc. Exp. Biol. Med., 38: 254-256, 1938. 
Caminopetros, J. Sur la faune des phlebotomes de la Grece. Bull. Soc. Path. 

Exot., 27: 450-455, 1934. 
Chagas, A. W. Infec^ao de Phlebotomus intcrmed'ms pela Leishmania chagasi. 

Brazil Med., Rio de Janeiro, 53: 1-2, 1939. 
Chagas, E., Cunha, A. M. da, ct al. Leishmaniose visceral americana. Mem. 

do Instit. Oswaldo Cruz, 32: 321-390, 1937. 
Christophers, S. R., Shortt, H. E., and Barraud, P. J. The anatomy of the sandfly 

Phlcbotomus argentipes Ann. and Brun. The head and mouthparts of the imago. 

Ind. Med. Res. Mem. No. 4: 177-204, 1926. 
Costa Lima, A. da Sobre os phlebotomos americanos. Mem. do Instit. Oswaldo 

Cruz, 26: 15-69, 1932. i 

**Dicke, R. J., and Hsiao, T. Epidemiology of kala-azar in China. NAVMED, 

930, 1946. 

Doerr, R., Franz, K., and Taussig, S. Das Pappatacifieber. Leipzig, 1909. 
Dyar, II . G. The present knowledge of the american species of Phlebotomus 

Rondani. Amcr. Jl. Hyg., 10: 112-124, 1929. 
Floch, H. Phlebotomes de Guyane franchise. I-XV. Pub. Inst. Pasteur Guyane, 

1941-1945. 
, and Abonnenc, E. Clef d'identification de 140 Phlebotomus males du 

nouveau continent. Bol. Ent. Venz., 6: 1-24, 1947. 
Franca, C., and Parrot, L. Introduction a 1'etude systematique des Dipteres du 

genre Phlebotomus. Bull. Soc. Path. Exot., 13: 695-708, 1920. 
**Hertig, M. Phlebotomus and Carrion's disease. Amer. Jl. Trop. Med., 22 

(Suppl.), 1942. 
, and Fairchild, G. B. The control of Phlebotomus in Peru with DDT. Ibid., 

28: 207-230, 1948. 



248 MEDICAL ENTOMOLOGY 

Hoare, C, A. Early discoveries regarding the parasites of oriental sore. Trans. 

Roy. Soc. Trop. Med. Hyg., 32: 67-92, 1938. 
* . Cutaneous leishmaniasis. A critical review of recent Russian work. 

Trop. Dis. Bull., 41: 331-345, 1944. 
Kirk, R., and Lewis, D. J. Taxonomy of the Ethiopian sandflies. Keys for the 

identification of the Ethiopian species. Ann. Trop. Med, Parasit., 40: 117-129, 

1946. 

Larrouse, F. Etude systematique et medicale des phlebotomes. Paris, 1921. 
Lindquist, A. W. Notes on the habits and biology of a sand fly, Phlebotomus 

diabolicus Hall, in southwestern Texas. Proc. Ent. Soc. Wash., 38: 29-32, 1936. 
*Malamos, B. Leishmaniasis in Greece. Trop. Dis. Bull., 44: 1-7, 1947. 
Mangabeira, F., and Galindo, P. The genus Phlcbotomus in California. Amer. 

Jl. Hyg., 40: 182-198, 1944. 
Mangabeira, O. Contribui9ao ao estudo dos flcbotomus. Mem. Instit. Oswaldo 

Cruz, vols. 36, 37, 1941, 1942. A series of papers. 
Napier, L. E., et al. The transmission of kala azar to hamsters by the bite of 

the sandfly, Phlebotomus argentipes. Ind. Jl. Med. Res., 21: 299-304, 1933. 
Noguchi, H., et al. Etiology of Oroya fever. The insect vectors of Carrion's 

disease. Jl. Exp. Med., 49: 993-1008, 1929. 
Orsini, O. Leishmaniose em Minas Geraes. Brasil-Medico 54 (6): 762-766, 

1940. 
Patton, W. S., and Hindle, E. The north China species of the genus Phlebotomus. 

Proc. Roy. Soc., B, 102: 533-551, 1928. 
Sabin, A. B., et al. Phlebotomus (pappataci or sandfly) fever; a disease of military 

importance. Summary of existing knowledge and preliminary report of original 

investigations. Jl. Amer. Med. Assoc., 125: 603-606, 693-699, 1944. 
Sergent, Edm., et al. Revue historique du probleme de la transmission des 

leishmanioses. Bull. Soc. Path. Exot., 26: 224-248, 1934. 
Shannon, R. C. Entomological investigations in connection with Carrion's 

disease. Amer. Jl. Hyg., 10: 78-111, 1929. 
Sinton, J. A. Some new species and records of Phlebotomus from Africa. Ind. 

Jl. Med. Res., 18: 171-193, 1930- 
. Notes on some Indian species of the genus Phlebotomus. Diagnostic tables 

for the females of the species recorded from India. Ibid., 20: 55-72, 1932. 

** . Diagnostic tables for the males. Ibid., 21: 417-428, 1933. 

Smith, R. O. A., Haider, K. C., and Ahmed, I. Further investigations on the 

transmission of kala azar. I-IV, VI. Ibid., 28: 575-579> 5 8l ~5 8 4> 5 8 5~59 I > 

1940; 29: 783-787, 799-802, 1941. 
9 et al. Identification of larvae of the genus Phlebotomus. Ibid., 21: 66 1- 

667, 1934. 
,ctal. Bionomics of P. argentipes. I, II. /&</., 24: 295-308, 557-562, 1936. 



THE PSYCHODIDAE 249 

Sun, C. J., and Wu, C. C. Notes on the study of kala-azar transmission. Chinese 

Med. Jl., 52: 665-673, 1937. 
Swaminath, C. S., Shortt, H. E., and Anderson, L. A. P. Transmission of Indian 

kala-azar to man by the bites of Phlcbotomus argentipes. Ind. Jl. Med. Res., 

30: 473-477, 1942. (First successful transmission from man to man.) 
Theodor, O. On African sandflies. Bull. Ent. Res., 22: 469-478, 1931. 
. Observations on the hibernation of Phlebotomus papatasii. Ibid., 25: 459- 

472, 1934. 
. On some sandflies (Phlebotomus) of the sergenti group in Palestine. Ibid., 

38: 91-98, 1947. 
. Classification of the old world species of the subfamily Phlebotominae. 

Ibid., 39: 85-116, 1948. 
Townsend, C. H. T. A Phlcbotomus the practically certain carrier of verruga. 

Science, n.s., 38: 194-195, 1913. 
. Progress in the study of verruga. Transmission by bloodsuckers. Bull. 

Ent. Res., 4: 125-128, 1913. 
. The transmission of verruga by Phlcbotomus. Jl. Amer. Med. Assoc., 61: 

1717, 1913. 
. The vector of verruga, Phlcbotomus vcrrucarum sp.n. Ins. Ins. Mens., i: 

107-109, 1913. 
. Human case of verruga directly traceable to Phlebotomus verrucarum. 

Ent. News, 25: 40, 1914. 
. On the identity of verruga and Carrion's fever. Science, n.s., 39: 99-100, 

1914. 
. The history, etiology, transmission of Peruvian verruga with an outline 

of the asexual cycle of its causative organism. West Coast Leader, Lima, Mar. 

8, 1927. 
Unsworth, K., and Gordon, R. M. The maintenance of a colony of Phlebotomus 

papatasii in Great Britain. Ann. Trop. Med. Parasit., 40: 219-227, 1946. 
Wu, C. C., and Sun, C. J. Notes on the study of kala-azar transmission. Chinese 

Med. JL, Suppl. 2: 579-591, 1938. 
Yao, Y. T., and Wu, C. C. Notes on the Chinese species of the genus Phlebotomus. 

Sandflies of Hainon Island. Trans. Cong. Far East. Assoc. Trop. Med. (loth 

Cong., Hanoi, 1938). 
, and Wu, C. C. Sandflies of Nanning and Tienapo, Kwangsi. Chinese 

Med. JL, 59: 67-76, 1941. 



CHAPTER X 



Mosquitoes: Their Structure, 
Biology, and Classification 



Culicidae or mosquitoes are easily recognized by their characteristic 
JL wing venation and the presence of a fringe of scales on the posterior 
margin of the wing and on the veins (Fig. 93). They are slender, soft- 
textured flies with long antennae (Fig. 95). The segments of the antennae 
bear whorls of hairs; in most of the males the whorls of hairs are so dense 




2da 



Fig. 93. Wing of Anopheles walJ(eri labeled according to the Comstock-Needharn 
terminology, with the usual terms employed by dipterists in parentheses. The veins: 
C, costal; Sc, subcostal (auxiliary); Ri (ist longitudinal): Rz and Ra (2nd longitudinal); 
R< + 5 (yd longitudinal); Mi + 2 (qth longitudinal); GUI -f- Cua ($th longitudinal); ada 
(6th longitudinal); r-m, radio-medial cross-vein (anterior cross-vein); m-cu, medio- 
cubital cross-vein (posterior cross-vein). The cells: a, Sc (subcostal) ; b, Ri (ist marginal) ; 
c, Ra (2nd marginal); d, Ra (submarginal); e, Rs (ist posterior); f, Ma (2nd posterior); 
g, Ms (yd posterior); h, GUI (qth posterior); i, ist A (anal cell); j, 2nd A (axillary 
cell). (After Matheson.) 

as to give the antennae a bushy appearance (Fig. 96). The family is divided 
into two subfamilies: the Chaoborinae in which the mouth parts are short 
and not adapted for piercing; and the Culicinae in which the mouth parts 
are, in most species, fitted for piercing and sucking blood. Not all the species 
of the Culicinae take blood; the males do not take blood. 



MOSQUITOES 251 

The larvae of the Culicidae are all aquatic. In the Chaoborinae the larvae 
are predaceous, the antennae being modified for grasping organs (Fig. 94). 1 
In the Culicinae the antennae are not so modified and food is obtained by 
the action of the mouth brushes (Fig. 107). The thorax consists of three 
fused segments, always wider than the abdomen. The abdomen consists of 
nine segments and is without appendages. The eighth segment bears a pair 




Fig. 94. Larva of Chaoborinae. Upper: Larva of Mochlonyx cinctipes. Center: Chao- 
borus punctipennis. Lower: Eucorethra under woodi. A, air sac; Ant, prehensile antennae. 

of spiracles, either at the end of a long tube, the siphon (Fig. 105) or the 
siphon may be absent (Fig. 106). The pupae of the Culicinae are all aquatic, 
active, comma-shaped. The anterior portion (cephalothorax) is enlarged and 
provided with a pair of horns or trumpets, the respiratory organs (Fig. 103). 
The abdomen consists of eight segments (nine or ten are recognized), the 
eighth segment bears a pair of paddles and each paddle has a midrib. 



1 The Chaoborinae are not further treated here. 



MEDICAL ENTOMOLOGY 




Fig. 95. Aedes vexans, female. ABD, abdomen; ANT, antenna; E, eye; F, femur; 
H, haltere; MES, mcsonotum; MXP, maxillary palpus; PB, proboscis; SCT, scutellum; 
TB, tibia; TAR, tarsus with its five segments. 



MOSQUITOES 




Fig. 96. Aedes vexans, male. Lettering as in Fig. 95. 



254 MEDICAL ENTOMOLOGY 

THE STRUCTURE OF MOSQUITOES 
THE ADULT 

The more general features of an adult mosquito are shown in figures 95,96. 
The head is nearly globose and is borne on a slender neck. The compound eyes 
are prominent, large, and occupy most of the lateral areas of the head; the 
ocelli are lacking. The small median area between the eyes is called the ver- 
tex while the broader portion back of the vertex is generally known as the 
occiput. The front or frons lies in front of the vertex and bears the antennae. 
Anterior to the frons and separated from it by a suture is the clypeus, a short, 
usually nude, snoutlike projection (Fig. 97 Clp). The antennae arise on the 
sides of the frons between the eyes. Each antenna consists of 15 segments. The 
first, the scape, is very small and hidden beneath the large, globular second 
segment, the torus. The remaining segments (13) are filamentous and form 
the flagellum. Each segment, except the first, of the flagcllum has a basal whorl 
of hairs, which are usually long and bushy in the males (Fig. 96) and shorter 
and sparser in the females (Fig. 95). 

THE MOUTH PARTS : In the female the mouth parts (Fig. 97) consist of 
an elongated proboscis within which lie the piercing stylets. The proboscis is 
the labium (Lb), a hollow cylindrical tube, narrowly open along its dorsal 
face and terminating in two pointed lobes, the labellae. The stylets within the 
labium consist of (i) the labrum, 2 a long, sclerotized, sharply pointed rod 
that is grooved on its ventral surface; in cross section it appears U-shaped, the 
opening of the U closed by a delicate membrane (Fig. 97) ; (2) the mandibles 
(md), a pair of delicate, linear-lanceolate structures lying close beside and 
behind the labrum; (3) the hypopharynx (Hphy), a thin lanceolate structure 
that is more or less closely applied to the thin mandibles and labrum; (4) the 
maxillae (Mx), a pair of thin, sclerotized shafts, each terminating in a some- 
what enlarged tip that bears a row of small, retrorse teeth; (5) a pair of 4 to 5- 
jointed maxillary palpi (MxPlp). The maxillary palpi arise at the anterior 
margin of the head, just beneath the clypeus. The palpi differ in the two sexes. 
In the females (Culicini) the palpi are much shorter than the proboscis; in the 
males 3 they are usually densely haired and generally longer than the pro- 
boscis, with the last two segments angled upward and tapered to a point 



2 This is often referred to as the labrum-epipharynx, but here we shall use the word 
labrum to indicate both structures. 

3 In the males of certain genera and in some species of other genera the palpi of both 
males and females are similar. 



MOSQUITOES 255 

(Fig. 125) . In the females of the Anophelini the palpi are straight and about 
as long as the proboscis (except in the genus Bironella) ; in the males the palpi 
are nearly as long as or longer than the proboscis while the last two segments 
are stouter, somewhat flattened, bent upward, and rounded at the apex (Fig. 




Fig. 97. Mouth parts of female mosquito. Lejt: Frontal view of the head of a mosquito 
with the mouth parts removed from the labium and the tips of the parts greatly enlarged. 
Center: Cross section and isometric view of the arrangement of the piercing parts. Right: 
A female in the act of taking blood. Ant, antenna; Clp, clypeus; F, food channel; Hphy, 
hypopharynx; L, labella; Lb, Labium; LbEp, labrum-epipharynx or simply labrum; md, 
mandible; MX, maxilla; MxPlp, maxillary palpus; Sc, salivary channel. 

The mouth parts of the male are greatly modified. The mandibles, when 
present, being greatly reduced, and the maxillae being thin and delicate and 
usually greatly reduced or almost absent. 

The action of the mouth parts in taking blood may be observed by allowing 
a mosquito to bite. When a satisfactory site is selected, the labellae are pressed 
close to the skin. By muscular action and pressure the cutting mouth parts 



256 MEDICAL ENTOMOLOGY 

are forced through the skin and soon all the mouth parts except the labium 
are deeply embedded; the basal half of the labium is bent back exposing the 
other mouth parts, and blood can be seen streaming up the food channel; 
the apical part of the labium still holds the piercing parts in the groove and 
undoubtedly steadies them. 

THE THORAX: The thorax is distinctly wedge-shaped, the base upper- 
most. The sides of the wedge form the pleura and the apex bears the legs. It 
is composed of three segments, the second and third being solidly fused to- 
gether. The spiracles appear as prominent black-rimmed apertures on seg- 
ments two and three. The prothorax (ist segment) is normally greatly 
reduced and consists of the two lobes located just back of the head (these 
lobes are usually widely separated when viewed from the dorsum), the 
postpronotum (Fig. 98 PPn) and the proepisternum (propleurum). The pro- 
sternum lies between the first pair of coxae. The second and third thoracic 
segments are solidly fused together as in most Diptera. The dorsal surface is 
composed almost entirely of the large mcsonotum and scutellum (dorsum 
of the second thoracic segment) ; back of the scutellum is the small, usually 
smooth postnotum (Fig. 98 9). The sides of meso- and metathorax are divided 
into several scleritcs. The names and position of these sclerites are fully ex- 
plained in Figs. 98 and 99. On these sclerites are certain setae or bristles that 
have been assigned definite names. They are of much importance and form 
landmarks for the placing of many of our species in their respective genera. 
These groups are as follows (Figs. 98,99) : (i) pronotal group (Pn), a varying 
number of setae massed on the pronotal lobes; (2) proepisternal or propleural 
group (Ps), a single stout seta or a mass of them on the proepisternum; (3) 
postpronotal group (PPn), one or several setae arranged more or less in a 
row just in front of the ridge on the posterior margin of the postpronotum; 
(4) spiracular group (Sp), a row of setae just in front of the anterior spiracle 
and behind the postpronotal ridge; (5) postspiracular group (P Sp), a num- 
ber of setae located on the upper portion of the mesanepisternum and directly 
behind the anterior spiracle; (6) prealar group (Pa), a small group on the 
dorsoposterior projection of the sternopleuron ; (7) sternopleural group (St P), 
a group consisting of a variable number of setae located near the posterior 
margin of the sternopleuron and often crossing it (the location of these setae 
varies); (8) upper mesepimeral group (UMe), a group located on the upper 
portion of the mesepimeron; and (9) lower mesepimeral group (LMe), one 
to several setae on the lower portion of the mesepimeron. 

The dorsal area of the thorax offers comparatively few characters of value 
in systematic work except coloration patterns and the arrangement of setae 



MOSQUITOES 



257 




Fig. 98. Lateral views of the thorax of mosquitoes. (/) Uranotaenia lowii. (2) Culiseta 
morsitans. (3) Anopheles punctipcnnis. (4) Psorophora ciliata. (5) Megarhinus septen- 
trionaUs. The sclerites of the thorax (2) : i, pronotum (prothoracic lobe) ; 2, proepister- 
num; 3, postpronotum; 4, mesanepisternum; 5, sternopleuron; 6, mesepimeron; 7, mete- 
pisternum; 8, prealar area; 9, postnotum; 10, metepimeron; n, meteusternum; m, meron. 
The setae (4): LMe, lower mesepimeral; Pa, prealar; Pn, pronotal; PPn, posterior pro- 
notal or postpronotal ; Ps, proepisternal; P Sp, postspiracular; Sp, spiracular; St P, 
sternopleural; UMe, upper mesepimeral. The dorsal portion extending from I to 9 repre- 
sents the mesonotum (2). 



MEDICAL ENTOMOLOGY 




Fig. 99. Lateral views of the thorax of mosquitoes. (6) Orthopodomyia signi/era. (7) 
Deinocerites pseudes. (8} Wyeomyia smithii. (9) Culcx pipicns. (/o) Mansonia pcrtur- 
bans. (//) Aedcs vexans. Explanations as in Fig. 98. 

and scales. The scutellum is separated by a transverse suture from the mesono 
tum. In all the genera except Anopheles and Megarhinus the scutellum is 
trilobed, and each lobe generally bears stiff bristles and usually scales; in the 
above-named genera the scutellum is arcuate or rounded behind and the 
bristles arranged evenly on it. 



MOSQUITOES 259 

THE WINGS : The wings are long and narrow (Fig. 93) . The venation 
is characteristic and the presence of scales is very distinctive o this family. 
The scales are frequently of different colors or may be distributed so as to give 
definite patterns (Fig. 126). The terminology of the wing veins and cells 
varies. The Comstock-Needham system and that used by most dipterists is 
illustrated in Fig. 93. As the venational pattern varies very little throughout 
the family, the form, shape, and color of the scales and their arrangement 
frequently offer excellent characters in separating species (Fig. 131). The 
second pair of wings are represented by small knoblike structures, the halteres 
(Fig. 96 H). 

THE LEGS : The legs are long and slender (Fig. 96) . Each leg consists of 
the usual parts, coxa, trochanter, femur, tibia, and a 5-segmented tarsus. The 
coxa is short, stout, and connects with the ventral portion of the thorax. 
The trochanter is a small, short segment connecting the coxa to the long femur. 
The tibia is slender and about as long as the femur. The tarsus is usually 
very long and the segments vary in length, though the first one is much the 
longest. The last segment bears a pair of claws or ungues. The claws vary 
greatly in size and those of the hind legs are generally smaller than those of 
the other legs. In the females the claws are usually simple, that is, they do 
not bear teeth except in most species of the genera Aedes, Psorophora, Haema- 
gogus, Armigeres, and some others. In the males the claws of the first pair of 
legs (and sometimes also the second pair) are usually toothed, though in 
anophelines one claw is usually reduced and the other is toothed. In nearly 
all species there is present a small hairy seta (empodium) between the bases 
of the claws; in the genus Culex there is, in addition, a pair of thin padlike 
structures (pulvilli) beneath the claws that is diagnostic for this genus. 

THE ABDOMEN: The abdomen is narrowly elongate, nearly cylindrical, 
and consists of ten segments, the first eight of which are distinct. Each seg- 
ment is composed of a tergite that extends down the sides and is connected 
with the sternite by a pleural membrane. The successive segments are joined 
by thin membranes (intersegmental membranes). In all the culicines both 
the dorsal and ventral surfaces are usually covered with dense scales; in the 
anophelines scales are practically absent or present in restricted areas. Six 
pairs of spiracles are present on the second to seventh segments. In the 
female the abdomen is pointed, as in Aedes, or truncate, as in Culex. The 
ninth segment is reduced, and between it and the eighth lies the opening of 
the female reproductive organs. The tenth segment is greatly reduced and 
bears the cerci and anal opening. In the male the terminal abdominal seg- 



2 6o MEDICAL ENTOMOLOGY 

ments are modified for sexual purposes. Shortly after emergence from the 
pupa (usually within 24 hours) the eighth, ninth, and tenth segments un- 
dergo an axial torsion through an arc of 180 so that the dorsal surface be- 
comes ventral and the ventral dorsal. The tip of the abdomen back of the 
eighth segment is generally called the hypopygium, male genitalia, or, by 
some, terminalia. 




9T- 



Fig. 100. Male genitalia of Aedes stimulans. AL, apical lobe; BL, basal lobe of side- 
piece; BP, basal plate; C, claw or spine of clasper; Cl, clasper; Clsp, claspette; F, filament 
of claspette; IF, interbasal fold; L(), lobe of ninth tergite; Mes, mesosome; P, paramere; 
Sp, sidepiece; 108, tenth sternite; pT, ninth tergite. 

MALE GENITALIA: The structure of the male genitalia affords excellent 
characters for the identification of species and an understanding of these 
structures is essential. Figs. 100-102 show the main structures to be observed 
in the genera Aedes, Culex, and Anopheles. 

As the terminal segments (8th to loth) of the male abdomen undergo an 



MOSQUITOES 261 

axial torsion of 1 80, it is essential to remember that ventral becomes dorsal 
and dorsal ventral. The terms lower and upper will be used in their ordinary 
sense but all morphological terms as dorsal, ventral, and names of sclerites 
will be employed with their correct meaning. Typically the genitalia struc- 




L9 



Fig. 1 01. Male genitalis of Culex pipicns. Cl, clasper; D, dorsal bridge; L, leaf 
of subapical lobe; Lp, lobe of ninth tergite; Mes, mesosome; Si, subapical lobe; 
Sp, sidepiece; loS, tenth sternite or paraprocts; pT, ninth tergite; V, ventral 
bridge. 

tures begin with the ninth segment; this segment consists of a complete ring, 
more or less sclerotized, especially on the dorsal aspect. The tergite (9T, ixT) 
may possess lobes (Lp, T) or the lobes may be greatly reduced or almost 
absent. From within the ring of the ninth segment arises a pair of large, 
hollow, forcepslike appendages. The basal parts are stout and are called 



262 MEDICAL ENTOMOLOGY 

sidepieces, or coxites (Sp), or basistyles. The apical appendage of each is long 
and normally narrow (CL), or it may be expanded (Psorophora) or modified 
into the most bizarre shapes (Wyeomyia) ; it is called the clasper or dististyle. 
Each sidepiece may bear a basal lobe (Fig. 100 BL) or the lobe may be lacking 
or the lobe may be replaced by several stout spines (Fig. 102 Ps), parabasal 
spines. There may be an apical lobe (Fig. 100 AL), the lobe may be subapical 
in position as in Culex (Fig. 101, SI), or it may be absent. In anophelines there 
is usually present an internal spine (Fig. 102 IS). Arising from a basal fold that 
aids in uniting the sidepieces are the claspettes (Clsp) ; in the Culicini {Aedes, 
Psorophora, etc.; absent in the genus Culex} these structures may be very 
complicated; in the Anophelini they are represented by lobes, the outer or 
dorsal and inner or ventral lobes (Fig. 102 Dl and VI). In the median plane, 
lying directly above and extending beyond the ninth tergite are the sclerotized 
parts of the tenth segment (los), the proctiger. The structures here involved 
have been variously designated and differ greatly in the different genera. The 
tenth sternite (ios) is usually well developed in such genera as Aedes, Culex, 
Culiseta, Psorophora, Mansonia, and others. In Anopheles the tenth sternite 
is vestigial, only the membranous anal lobe (Fig. 102 Lb) being present. Be- 
tween the sternites and beneath them or the anal lobe is located the meso- 
some (Mes) or phallosome, a sclerotized tubelike structure surrounding the 
penis. It is supported and held in position by the basal plates (Fig. 100 BP) and 
the parameres (P). The mesosome varies greatly in the different genera and 
furnishes characters for the differentiation of genera and species. In Anopheles 
the mesosome is a long, slender tube with or without apical leaflets (Fig. 102) ; 
in other genera it may assume bizarre shapes as in Cul&P^Fig. 101). 

THE PUPA 

The pupa is the stage from which the adult emerges. All pupae are aquatic, 
active, take no food, and are comma-shaped (Fig. 103). The enlarged anterior 
half contains the future head and thorax of the developing adult. The more 
slender portion represents the abdomen and is composed of eight segments 
(nine or ten can be recognized) and a pair of paddles or fins (Fig. 103). 
Arising from the thorax is a pair of respiratory horns or trumpets, which 
break through the surface film of the water when the pupa float to the surface 
and permit air to enter through the spiracles located within the horns.) 

The abdomen of pupae is provided with various hairs and spines, and these 
have been studied by various workers in attempts to use them for identifica- 
tion purposes. Though a goodly number of pupae have been figured and 
described, the number is not sufficiently large to permit us to hope that species 




Fig. 102. Male genitalia of Anopheles quadrimaculatus. Upper: Lower or 
dorsal view. Lower: Lateral view. C, claw or spine of clasper; Cl, clasper; Clsp, 
claspettes; Dl, dorsal lobe of claspette; IS, internal spines; L, leaflets of meso- 
some; Lb, anal lobe; Mes, mesosome or phallosome; Ps, basal or parabasal 
spines of sidepiece; Sp, sidepiece or coxite; viiiS, ixS, eighth and ninth sternites; 
T, lobe of ninth tergite; viiiT, ixT, eighth and ninth tergites; VI, ventral lobe 
of claspette. 



264 MEDICAL ENTOMOLOGY 

identification by pupae may become well established. The characters most 
frequently used are the structure of the paddles and the arrangement of the 
hairs and spines. Anopheline pupae can usually be recognized in that spine 
A of segments 3 to 7 is stout, peglike, single, and located at the apical angles, 
while the same spine on segment 8 is in the same position and fringed. In other 
pupae spine A is usually branched and not located at the exact apical angle 
(Fig. 104). 




Fig. 103. Pupae of mosquitoes. Lejt: Aedes cinereus. Right: Anopheles punctipennis. 
P, paddles; R, respiratory horns. 

THE LARVA (Fourth instar) 

The larvae of all known species are aquatic and their structure adapts them 
to life in the water (Fig. 113). The larva (Figs. 105,106) is legless and con- 
sists of a prominent head, a large, boxlike unsegmented thorax, and a slender 
abdomen of nine segments. 

. The head is normally well sclerotized and bears the mouth parts, the an- 
tennae, eyes, the remarkable mouth brushes, and an arrangement of hairs 
or tufts. The mouth parts (Fig. 107) consist of a labrum (often referred to as 
the preclypeus), a pair of mandibles, a pair of maxillae, and the labium. These 
are typical mandibulate mouth parts. The mouth brushes are remarkable 
structures as by their vigorous and rapid movement they direct the food into 




Fig. 104. Pupal chactotaxy. Left: Typical arrangement of hairs of an anopheline. Right: 
Typical arrangement of hairs of a nonanopheline. The numbers and letters refer to the 
hairs on each abdominal segment. (After Penn.) 



2 66 MEDICAL ENTOMOLOGY 

the mouth cavity or serve to capture their prey (some Psorophora, Megar- 
hinus). It has been shown by Becker (1938), Cook (1944), and Farnsworth 
(1947) that the activity of the mouth brushes is due to muscular .action and 
elasticity of the cuticula. Fig. 107 illustrates the muscles and structures in- 
volved in this movement. The external and internal messorial muscles (aem, 
aim) by pulling the palatal bar to a more anterior position depress the mouth 
brushes. The median palatal muscle (mpa) would then contract and cause 
the brushes to return to their original position. Hence by the rapid action of 
these muscles along with the elasticity of the cuticula the mouth brushes are 
set in active vibration. (Consult Farnsworth, 1947.) 

The antenna consists of a single segment and it terminates in a hair and 
certain terminal spines; in the culicines subterminal spines are present. A 
tuft of hairs, a single hair, or a branched hair (the antennal hair tuft) is 
located near the middle of the shaft. The eyes are located on the sides of the 
head. The large anterior eyes are the developing eyes of the adult and back of 
them is located the small larval eyes. The various paired hairs on the head 
are given names, numbers, or letters according to the individual worker. In 
the culicine and anopheline larvae the principal head hairs are illustrated 
and named in Figs. 105 and no. 

The thorax bears a large number of hairs and they are so arranged as to 
indicate the pro-, meso-, and metathoracic segments. The usual numbers ap- 
pK ^d to these hairs or groups are shown in Figs. 105 and 109. In the anophe- 
lines the character of these hair groups is of considerable importance in the 
identification of species. Many of these have been given names, which are 
indicated under the illustrations. 

The abdomen consists of nine segments. On the dorsal surface of the eighth 
abdominal segment are the openings of the respiratory system, which, in all 
the Culicini, consists of a long siphon (Fig. 105 S) through which a pair of 
tracheal tubes run to the tip; these tracheae can be opened or closed by a series 
of apical valves which surround the spiracles; in all anophelines the siphon is 
absent and the spiracles open through a stigmatal plate (Figs. 106,109). The 
ninth segment is usually more slender, is attached ventroposteriorly to the 
eighth, and points ventrally and backwards. Its integument is more or less 
sclerotized forming the dorsal plate or saddle (Fig. 105 DP). This saddle may 
completely surround (ring) the segment (as in Psorophora, some Aedes) or 
be open along its ventral median face. Beyond the saddle the segment appears 
fleshy and bears at its tip the anal opening and four (rarely two) thin, taper- 
ing appendages, the tracheal or anal gills. In addition, the ninth segment bears 
two important structures, the dorsal brush, consisting of two sets of longer or 



LHT- 



Head 




YB 



Fig. 705. Dorsal view of larva of Aedcs stimulans. The eighth and ninth segments and 
the siphon are turned lateral so as to give a side view of them. A AT, anteantennal hair 
tuft; AG, anal gills; Ant, antenna; AT, antennal tuft; C, comb; DH, dorsal brush; DP, 
dorsal plate or saddle; E, eyes; LAT, lateral abdominal tufts; LHT, lower head tuft or 
hair; Mb, mouth brushes; P, pecten; S, siphon or air tube; SD, subdorsal hair tufts of the 
abdomen; SHT, siphonal or air tube tuft; St, stigma; UHT, upper head tuft or hair; 
VB, ventral brush; 1-9, segments of abdomen. The small numbers on thorax and segment 
4 of abdomen indicate the arrangement of the setae. 

267 



Head 




Fig. 106. Larva of Anopheles punctipennis. Cl, inner clypeal hairs; DP, dorsal plate; 
H, float hairs or palmate tufts; O, outer clypeal hairs; P, pecten; St, stigma of spiracle. 




Fig. 707. Mouth parts of a mosquito larva (Anopheles) . Upper: Ventral view of head. 
Lower left: A single mandible. Lower right: A maxilla. Ant, antenna; Lb, labium; M, 
mentum; MB, mouth brushes (see Fig. io8)\ Md, mandible; Mu, muscles of mandible; 
MX, maxilla; MxPlp, maxillary palpus; Sm, submentum. 



270 MEDICAL ENTOMOLOGY 

shorter hair tufts (Fig. 105 DB, only one set is shown; the other is on the 
opposite side) located at the posterodorsal angle; and, in most mosquito larvae, 
a ventral brush, consisting of unpaired hair tufts extending from the ventro- 




Fig. 108. Internal view looking down toward the mouth brushes to show the attach- 
ments that move the brushes. Aem, tendon attaching the external messorial muscle; Aim, 
same for the internal messorial muscle; Bib, base of brush; Lb, larval mouth brush; Lpp, 
lateral palatal plate; Mb, median bristles; Mes, messor; Ml, median lobe; Mpa, median 
palatal muscle; Ppb, posterior palatal bar; Ta, sclerite; Tg, transverse girdle. (After 
Farm worth.) 

apical edge to a greater or less distance forward; the distal tufts usually have 
sclerotized bases forming a sort of grid or barred area. In the culicines the 
siphon or air tube has one to several pairs of subventral hair tufts or a median 
row of hair tufts and, usually on the basal half, a paired row of short, spine- 
like teeth, the pecten (Fig. 105 P). In some genera the pecten may be absent. 



MOSQUITOES 271 

In all anophelines each side of the stigmatal structure has a sclerotized plate 
that bears a distal row of spines of varying length the pecten (Fig. 109) or, 
as it is sometimes called, the comb. The true comb is borne laterally on the 
eighth segment (Fig. 105 C) and is found in anophelines only in the first- 
stage larva. The comb consists of a patch of scales arranged in various ways. 
Each scale may be toothlike, fringed with spinules or with stout branches, and 
arise independently or be attached to a sclerotized plate. 




Fig. io(). Left: Dorsal view of spiracle of larva of Anopheles, Right: Pecten of larva of 
Anopheles, Ap, anterior plate or flap; Fl, lateral flap or ear; M, dorsal plate; Pip, posterior 
spiracle plate; Sp, spiracle. 

In recent years the chaetotaxy or arrangement of hairs and spines on the 
thorax and abdomen of mosquito larvae has been closely studied, and names 
or numbers or both have been assigned to them. Fig. no presents the num- 
bering system as interpreted by Hurlbut (1938) for anophelines, and Fig. 105 
shows similar numbers assigned by the author to culicines. However, there 
is great variation among workers and usually each author explains his system. 

THE EGG 

The eggs (Fig. in) of mosquitoes are rather characteristic and well pro- 
tected by several layers the thin vitelline membrane which surrounds the 
yolk (the chorion, exo- and endochorion) and a heavily sclerotized outer shell 
which externally is frequently patterned with small bosses or reticulations 
(Fig. 112). At the anterior pole is the micropyle, a minute opening for the 
entrance of the sperm; the micropyle is usually surrounded by a ring of small 
bosses forming a kind of rosette. The eggs of culicines are generally elongate 



272 



MEDICAL ENTOMOLOGY 




Fig. no. The chaetotaxy of the fourth instar larva of Anopheles wal^eri', the hairs are 
all numbered i to 14. (/) Thorax and first five abdominal segments; the right half is 
dorsal, the left ventral. (2) Leaflet of palmate tuft. (3) Leaflet of hair i of metathorax. 
(4) Leaflet of hair i of second abdominal segment (5) The spiracular apparatus, dorsal 
view. (6) Sixth and seventh abdominal segments; right dorsal, left ventral. (7) Dorsal 
view of head. (8) Ventral view of head. (9) Tip of antenna, (/o), (//), (72) Basal 
tubercles of pro-, meso-, and metathoracic pleural hairs. (73) Inner clypeal hair. (14) 
Anterior part of the frontoclypeus. (75) Tip of left maxillary palpus. (76) Lateral aspect 
of eighth, ninth, and tenth abdominal segments. (After Hurlbut.) 



MOSQUITOES 



273 




Fig. in. Eggs of various species of mosquitoes, (a) Egg mass of 
Culex pipiens. (b} Egg mass of Culiseta inornata. (<:) Egg of Aedes 
aegypfi. (d) Egg of Anopheles punctipcnnis, dorsal view. (<?) The 
same, ventral view. (/) Egg of Anopheles quadrimaculatus , dorsal 
view, (g) Egg of Anopheles crucians. (From Howard, Dyar, and 
Knab.) 




Fig. 112. Egg of A/iophclcs wal1(cri. E, chorion; F, frill; 
Fl, floats. (From Hurlbut.) 

oval and may be laid singly (as in Aedes) or in masses (as in many Culex 
spp.). The eggs of anophelines are strikingly different from those of the 
culicines. The egg is generally boat-shaped, flattened, slightly convex or con- 
cave dorsally, and strongly convex ventrally (Fig. 112). The chorion is modi- 
fied to form a frill, which partially or completely surrounds the upper portion. 



274 



MEDICAL ENTOMOLOGY 



In addition, a pair of characteristic floats or air sacs on each side enables the egg 
to float freely on the surface of the water (Fig. 112 Fl). The extent, arrange- 
ment of the floats, coloration, and certain other features have all been studied 
and have been found quite valuable in identifying species of Anopheles, espe- 
cially of closely related forms or races as A. maculipennis of Europe. Causey, 
Deane, and Deane (1944) nave studied the eggs of thirty Brazilian species of 
anophelines and have been able to identify species on egg characters. 




f'S- "3- Larvae of mosquitoes (Acdcs spp.) resting and feeding at the surface of the 
water; note the long ana! siphon or breathing tube; note the curled up pupae among 
them. 

THE BIOLOGY OF MOSQUITOES 

All mosquitoes undergo a complete metamorphosis, i.e., from the egg hatches 
a larva which feeds and grows; the larva, when mature, transforms into an 
active pupa (Fig. 113); from the pupa there later emerges the adult. The 
larval and pupal stages occur only in water (Fig. 113). The eggs of all known 
species are laid on water, near water, or in places where water is likely to be 
at some later date (as in many Aedes spp., Psorophora spp., and some others). 
All mosquito larvae molt four times, the last molt disclosing the pupa. In the 
study of the larva the fourth instar, which is the stage before the last molt, is 
called the mature larva, and it is this stage that is used almost exclusively for 



MOSQUITOES 275 

identification purposes. Studies on the earlier stages have been made, but not 
much success has resulted in identifying species except in certain small groups. 
It is not our purpose here to give an extended account of mosquito bionomics. 
The literature in this field is so vast and has increased so enormously during 
the past few years that the reader must consult special papers dealing with 
groups or individual species. For our North American species consult King, 
Bradley, and McNeel (1942), Matheson (1944), or Carpenter, Middlekauff, 
and Chamberlain (1946). The following account is mainly concerned with 
those species known to be or suspected of being transmitters of important 
diseases. 

CULICINE MOSQUITOES 

The vast majority of our species belong in the tribes Culicini and Sabethini 
and are generally referred to as the culicine mosquitoes. 

THE GENUS CULEX: Probably one of the most abundant, most wide- 
spread, and generally conceded most annoying mosquitoes is one that belongs 
to the genus Culex, the common house mosquito Culex pipiens Linn. 4 (Fig. 
114). Not only is it annoying by its bites but it is the transmitter of several im- 
portant diseases of man and other animals. 

The house mosquito is widely distributed throughout the Holarctic region; 
in South America it is found south of the 39th parallel of latitude, in East 
Africa from Egypt south to the Cape and west to eastern Belgian Congo, in 
Madagascar, and probably in other regions. This species passes the winter as 
fertilized females, hibernating in various shelters such as attics, cellars, cow- 
sheds, stables, and outbuildings of all kinds where protection, adequate mois- 
ture, and semidarkncss are found. The males all die with the approach of 
winter. It is probable that, in the warmer portions of the range of this species, 
continuous breeding may occur, though at a much reduced rate as indicated 
by several recent workers. In the temperate regions hibernation is the general 
rule. Enormous numbers of females may pass the winter in very small shelters. 
I have estimated from careful counts of definite areas that over 100,000 hiber- 
nated in a small dark cellar not over four feet by six feet with a height of only 



4 According to Marshall (1938) and other European workers this species rarely feeds 
on man but mainly on birds. They state that another species, so closely similar that it is 
difficult to recognize it, is the troublemaker. To this species has been assigned the name 
Culex mo/estus Forskal. This is the one that prefers mammalian blood but can reproduce 
generation after generation without blood ("autogeny"); C. pipiens requires blood for 
egg development and it prefers the blood of birds. 



2 7 6 



MEDICAL ENTOMOLOGY 




Fig. //f Culex piplens. Female. 



MOSQUITOES 277 

seven feet. Scarcely a pin point could be found on which a mosquito did not 
cling to ceiling, walls, hanging ropes, and a pump, which occupied the center 
of the small room. During the cold weather the hibernating individuals show 




Fig. 7/5. Breeding places <>i iiiirqniiucs. Upper: View across a marsh area 
with many pools and sluggish streams in which breed Aedes vexans and Ano- 
pheles pnnctipcnnis. Loner: A hog wallow where Aedes vexans and Culex 
pipiens breed in enormous numbers. 

little activity though occasionally they may invade the warmer rooms in search 
of blood. With the approach of spring, activity is resumed and the females 
seek suitable places for oviposition. Depending on the locality, egg laying 
begins in May or June or possibly earlier. Each female deposits from 100 to 



278 MEDICAL ENTOMOLOGY 

400 or more eggs in a boat-shaped mass (Fig. in a) on or close to the surface 
of standing water well protected from the winds. Each egg is cylindrical and 
tapers to the end away from the water. The favorite breeding grounds are 
rain-water barrels, cisterns, tanks, garden pools stocked with aquatic plants, 
slow-flowing polluted streams, flooded latrines, cesspools, polluted ponds (Fig. 
115), catch basins, sagging gutters, and almost any water-filled container. 

Depending on the temperature, the eggs hatch in from one to three days 
or occasionally longer. The young larva escapes from the lower end of the egg 
and swims actively about in the water. During warm weather the larval de- 
velopment is very rapid, the pupal stage being reached in seven to ten days. In 
cold weather, larval development may be greatly delayed. The larvae (Fig. 
116) are very active, swimming with ease and rapidity by sudden jerks of the 
body. Being somewhat heavier than water, they rise to the surface by a rapid 
wriggling of the body from side to side, break through the surface film with 
their air tubes, and rest, the body sloping at an angle. During all this time, 
the mouth brushes are in motion, sweeping small particles into the alimentary 
canal along with a certain amount of water. 

The pupal period is short, usually only two or three days. The pupa nor- 
mally rests at the surface, the air tubes piercing the surface film. When dis- 
turbed, it swims rapidly downward by means of violent abdominal contrac- 
tions. The tip of the abdomen is provided with two broad paddles, which 
greatly aid in pupal movement. Being lighter than water, the pupa, when 
quiet, rises to the surface again. As the time for the emergence of the adult 
approaches, the pupa, when disturbed, descends with difficulty and rises more 
rapidly. The time occupied in the transformation from pupa to adult is very 
short. The pupa will be seen to straighten out the abdomen and air appears 
between the pupal skin and the adult. The pupa now seems almost silvery 
white, and its specific gravity being greatly reduced, the whole cephalothorax 
and part of the abdomen touch the surface. The pupal skin now splits in the 
median line of the cephalothorax and the dorsum of the adult appears in the 
slit. By constant pressure the slit widens and two transverse slits appear on 
each side. Slowly the adult works its way out, using the pupal skin as a float 
and balancing itself with great care. In two or three minutes the insect, now 
swollen with engorged air, stands poised on its previous prison cell, and is 
soon ready for its initial flight. At first the adult is almost colorless, but in a 
few hours the permanent color pattern appears. 

The entire life cycle from egg to adult occupies from 10 to 14 days. Genera- 
tion after generation follows throughout the summer season and breeding only 
stops with the approach of cold weather. Culex pipicns may be found breeding 



MOSQUITOES 



279 




Fig. ii 6. Larva of Culex pipiens. 



2 8o MEDICAL ENTOMOLOGY 

as late as November in the region of central New York, it is one of our domestic 
mosquitoes, that is, it breeds and lives in close proximity to human habitations. 
In the tropical and subtropical regions of the world it is replaced by Culex 
jatigans Wied. (quinqucfasciatus Say), a closely allied species. It is not always 
possible to separate these two species; reliance must be placed on a study of the 
male genitalia, and even this may not be satisfactory where the two species 
overlap. The larvae are practically identical. Both species breed in similar situa- 
tions, invade houses, bite during the evening hours and at night. The tropical 




Fig. 7/7. A productive roadside pool in western Canada. In early spring 
Aedes spencer ii is present, followed by A. vexans and A. dorsalis; later in Au- 
gust A. spcncerii, Culex tarsalis, and Culiseta inornata are found. (After 
Rcmpel.) 

species is said to be intensely anthropophilic (NAVMED, 983. 1946) and has 
a recorded flight range of three to four miles. 

Culex tarsalis Coquillett is easily recognized by the broad apical and basal 
white bands on the hind tarsi, the tibiae with apices and bases banded with 
white, and a broad whitish ring on the proboscis. In addition, the femora and 
tibiae have narrow longitudinal lines of white scales on outer and inner sides 
and a series of black V-shaped markings on the ventral surface of the abdomen. 
This is a very important species as it probably is the important vector of 
encephalitis of man and animals in North America. It has a wide distribution 
throughout the western United States and western Canada, especially in the 
plains. Freeborn (1926) reports it as the most widespread mosquito in Cali- 



MOSQUITOES 281 

fornia; Rees (1943) regards it as a major pest in Utah because of its abundance 
and wide distribution; Rempel reports it very abundant some years in Sas- 
katchewan; Cox (1944) states it is widespread and abundant in Texas. Its 
general distribution is southern British Columbia eastward through the Cana- 
dian prairie provinces to Michigan, south through the central, southern, and 
western states and Mexico. The adults are fierce biters and readily enter houses, 
normally attacking at dusk and after dark. The common breeding places are 
in fresh or foul ground pools (Fig. 117), roadside ditches, irrigation water, 
rain barrels, and similar situations. 

The genus Culex includes a large number of species placed in several sub- 
genera. Many of the species are vectors of filariasis (see p. 562), some of Japa- 
nese B encephalitis as Culex pipiens fallens and C. tritaeniorhynchus (natural 
infection), others of St. Louis encephalitis, western and probably eastern 
encephalomyelitis of horses, and encephalitis of man. However, most of the 
species of Culex occur in the tropical and subtropical regions, and the relation 
of these species to their hosts, in most cases, is not known. Edwards (1932) 
listed 317 species, and since then over 100 new species have been described, but 
comparatively little is known of their biology. 

THE GENUS AEDES: This genus contains a large number of species. In 
1932 Edwards listed some 410 species, and since then over 100 new species have 
been recognized. The species are frequently abundant, and the adult^may 
occur in vast numbers, especially in the Arctic regions, the subtropical regions, 
and the north temperate zone. They are distributed from the polar regions 
to the tropics and to high elevations in mountainous areas. Certain species as 
A. sollicitans and A. taeniorhynchus (breeding in tidal areas along seacoasts) ; 
A. stimulans, A. excrucians, A. punctor, A. communis, and others (in north 
temperate wooded areas) ; A. vexans, A. sticticus, and A. lateralis (some of our 
flood-water species); A. spcncerii, A. dorsalis, A. campestris (on the open 
plains) ; A. nearcticus and A. nigripes (in the Arctic regions) ; and A. ventro- 
vittis and others (in high mountainous regions) often render life almost un- 
endurable at certain seasons of the year. Not only do Aedes species act as pests, 
but a goodly number serve as efficient vectors of diseases of man and animals 
(see Table 8). 

It is not easy to briefly summarize the biology of the numerous species in- 
cluded in this genus. Edwards (1932) has given a general summary based on 
the various subgenera that he recognizes. In brief we may say the eggs are 
spindle-shaped or elliptical, thick-shelled, resistant to drying to a marked 
degree, and id singly not on or in water but in places where water will be 
either by rains, melting snows, tidal areas, or flood waters, in tree holes, bamboo 



282 



MEDICAL ENTOMOLOGY 



stumps, etc. As the eggs are very resistant they may ie dormant for several 
years (as for example A. vexans and A. sticticus). The larvae occur in various 
types of breeding places, and such places can be largely indicated by knowing 




Fig. ii 8, Upper: A deep woodland pool in which Aedes stimulans, A. fitchii, 
and A. cxcrucians breed in immense numbers. Lower: A shallow woodland 
pool where Aedes stimulans, A. fitchii, A. excrucians, A. intruders, A. tri- 
churus, and A. canadcnsis breed. 

the subgenus to which the species belongs. Most of the larvae are bottom 
feeders though a few are predaceous (species of the subgenus Mucidus). 

The species of the subgenus Ochlerotatus are world-wide in distribution, and 
they breed in temporary ground pools formed by rains, melting^ snows, flood 



MOSQUITOES 283 

waters, and tidal marshes; a few in tree holes. Examples: A. (0.) taeniorhyn- 
chus and others in tidal marshes in the Americas; A. (O.) vigilax, coastal areas 
of Australia and nearby islands; A. (0.) mariac in sea-water pools along the 
Mediterranean coasts; A. (0.) stimulant, A. (0.) fitchii, A. (0.) communis, 
A. (O.) trichurus, and others in snow-water pools in northern North America 
(Fig. 118). In the subgenus Finlaya practically all the species breed in tree 
holes (Fig. 119), bamboo stems, leaf bases of various plants, potholes in stream 
beds, coconut husks, banana stumps, pitcher plants, and a few species from 
grassy pools. Examples: A. (F.) triseriatus, A. (F.) alleni, and A. (F.) vari- 




Fig. 7/9. Left: A sycamore log which was cut for the honey; now filled with water. 
In this tree hole breed Anopheles barberi, Aedcs triseriatus, Culex apicalis, and C. res- 
tuans. Right: A tree hole in which Acdes triseriatus breed. (Both at Ithaca, New York.) 

palpus in North America, and many species in practically all parts of the 
world. The subgenus Stegomyia is practically confined to the tropical and 
subtropical regions of Africa, the Oriental region, and the Australasian region, 
though certain species, as Aedes (5.) aegypti, have been carried by commerce 
to nearly all parts of the world where they can find satisfactory breeding 
grounds. This subgenus was rather extensively studied in the western and 
southwestern Pacific regions during the recent war. Many new species have 
been described and old species broken down into a number of distinct species. 
Edwards (1932) lists 41 species from the world, and some 20 new species have 
since been described. This is an important group of mosquitoes. The principal 
breeding places are tree holes, leaf bases, coconut shells, artificial containers 
(as in A. aegypti) , and similar situations. The adults of most species are day 
.fliers. Though the subgenus Aedimorphus has over 50 species, only one is of 



284 MEDICAL ENTOMOLOGY 

major importance. A. (A.) vexans is world-wide in distribution and a pest 
wherever it occurs in abundance. Most of the species breed in temporary ground 
pools or flood waters. The subgenus Aedes occurs primarily in the Oriental and 
Australasian regions. Only one species, A. (A.) cinereus occurs in Europe and 
America. It breeds in early spring pools. The other subgenera consist of few 
species and very little is known about them. 

Aedes (Stegomyia) aegypti Linn. (Stegomyia jasciata, Aedes argenteus, 
Aedes calopus, etc.) : The yellow-fever mosquito (Fig. 120) is probably the 
most domesticated of any species; it is found only about human habitations 
and primarily lives in our houses. It has a wide distribution in the tropical and 
subtropical regions. It is found in most countries lying between latitudes 45 
North and 40 South, and its presence in temperate regions beyond these 
limits is of a temporary nature. According to Howard, Dyar, and Knab (1912), 
"Its permanent distribution is determined by the minimum temperatures and 
its temporary distribution by the maximum temperatures of any given region 
wherever it is sufficiently populated." Carter (1931) agrees with this view. 
The minimum temperatures are those that kill the hibernating eggs or prevent 
their development, and the maximum temperatures are those that permit the 
larvae to develop and the adults to flourish. Carter does not give these ranges of 
temperatures, though it is generally stated that in those areas where the nights 
are cool (68F. and below), as in California, the mosquito does not occur even 
if in the daytime the temperatures are sufficiently high to be subtropical. Hindle 
gives the permanent distribution as confined between the two isothermal 
lines of 20 C. (68 F.). 

The species can be recognized easily by the characteristic curving white lines 
on the thorax and the white banding of the tarsi. Though it has generally been 
considered an American species that has spread by way of commerce to all 
parts of the tropics, many workers now concede that it was originally an 
Ethiopian species brought to the Americas by the early navigators. The place 
of origin is of significance with regard to the origin and spread of yellow fever. 

LIFE HISTORY: The eggs (Fig. me) are laid singly on the water, just at the 
edge of the water, or on the sides of the container above the surface of the 
water. As the eggs can withstand drying for a long time, at least over five 
months, the filling of the receptacles by rain or otherwise assures the young 
larvae an adequate water supply for their short larval life. The eggs hatch 
in two days or less, if the temperatures are high, but hatching may be prolonged 
when the weather is cool, as during the winter months. The larval life is com- 
paratively short, occupying six to ten days, or it may be greatly prolonged by 




Fig. 120. The yellow-fever mosquito, Aedcs aegypti. 

cool weather. The mature larva (Fig. 121) is robust, rather stout, with a com- 
paratively short, somewhat pointed siphon. The siphon bears a pair of small 
hair tufts just beyond the pecten. The scales (8 to 12) of the comb are rather 
distinctive sole-shaped with a long, curving apical spine and several sub- 
apical spines (Fig. 121 2). The larvae are very responsive to disturbances of 
any kind, darting to the bottom of the water at the slightest disturbance or 
from a passing shadow. On account of this habit their presence is often diffi- 



286 



MEDICAL ENTOMOLOGY 




Fig. 121. Larva of the yellow-fever mosquito, Acdcs aegypti. (2) One of the teeth 
from the comb, greatly enlarged. 



MOSQUITOES 287 

cult to detect unless the inspector can take time to observe them as they quietly 
return to the surface or unless he empties out the container. Even then they 
may be missed as the larvae press themselves close to the bottom and are not 
easily dislodged. This burrowing habit frequently enables them to breed 
continuously in containers of drinking water which are frequently emptied 
and refilled, since many of them escape being poured out. 

The pupal period is very short, not over two days under normal conditions. 
The entire life cycle may be passed in ten clays, though ordinarily the time 
required varies from eleven days to three weeks. Within its permanent range 
it breeds throughout the year; generation succeeds generation with great 
rapidity when water, the necessary warmth, and a blood supply are available. 
During the colder months of the year the reproductive rate is slowed down or 
the eggs may remain dormant for a considerable period; the dry season may 
be passed in the egg stage. 

The adults, on emerging, mate within a few hours or a few days. Mating 
takes place while in flight. The female must now secure a blood meal in order 
that her eggs may develop. If blood cannot be obtained the eggs remain unde- 
veloped even though she feeds on honey, nectar, etc., and continues to live for 
a long time. The obtaining of a blood meal initiates ovarian development, and 
a steady source of blood enables the females to produce the maximum number 
of eggs. Each female is capable of laying from 50 to as many as 150 eggs during 
her lifetime. The females actively seek blood. They are primarily diurnal in 
their feeding habits and bite in bright sunlight. The times of greatest activity 
are the morning and evening hours, though I have had them feed on me 
consistently after dark in a lighted office where we were breeding them in 
quantity. The song of the yellow-fever mosquito is very feeble and it prefers to 
attack under cover, as about the ankles, under coat sleeves, at the back of the 
neck, and in similar places. 

The adults can remain alive for long periods, at least nearly four months or 
even more, when properly fed and kept under conditions ensuring moisture 
and warmth. The length of the adult life is of great importance in relation to 
the spread of yellow fever. In the open the adult life is probably not so pro- 
longed as four months, but on this point we have no very exact data. The 
range of flight is another important problem. It has generally been held that 
they do not fly over 100 yards from their breeding. Dunn (1927) records this 
species as breeding in water containers 500 yards from any habitation; this 
would indicate a flight range of at least that distance. Shannon and Davis 
(1930), in a series of well-planned experiments, obtained a flight range of 300 
io 350 meters (13 mosquitoes captured); 950-1000 meters (7 mosquitoes 




288 MEDICAL ENTOMOLOGY 

taken); a full 1000 meters (i mosquito obtained). In these experiments some 
32,000 adults were employed and less than 0.4 per cent were recovered. 

BREEDING PLACES \ The primary breeding place is in water held in artificial con- 
tainers in and around human habitations. These mosquitoes never breed in 
swamps, pools, or temporary puddles, even though these are located near 
houses. The more common types of water containers are rain-water barrels, 
wells, cisterns, tanks, sagging roof gutters, water-closet tanks, tin cans, vases 
with flowers, urns in cemeteries (Fig. 122), etc., in fact, in any type of artificial 
container capable of holding water; they also breed in tree holes (probably 

their original breeding ground), 
holes in stumps, water held by 
bromeliads, in the still-folded 
leaves of banana plants, and in 
similar situations. Dunn (1927) 
found them breeding in such 
numbers in tree holes (and some 
of the tree holes were at least 300 
yards from houses) that he con- 
sidered this type of breeding 
Fig. ;_v. View of a UnKil orouiul in the south- ground of importance in control 
ern United States. In each niche arc one or two wor ]^ fj e a j so f ounc l t h a t the 
flower vases, and Aedes aegypti breeds in them , , . .11. 

whenever water is present. e S s could remam viable in tree 

holes throughout the entire dry 

season in West Africa. He discovered them breeding in the water pockets at 
the bottom of crab holes about lagoons. It is said that the females prefer clean 
water for oviposition purposes, but the larvae have been found in nearly all 
types of polluted water. It would seem that water containing leaves is very 
attractive (Dunn). Though this species breeds almost exclusively in fresh 
water, it will occasionally breed in brackish water. Garnham et al. (1946) re- 
port finding it commonly throughout the forests in parts of Kenya breeding 
in rock holes along river beds in dry weather and in holes in recently felled 
trees. They further state that it is not common about human habitations in 
this region. 

Aedes (Stegomyia) albopictus (Skuse) is an important species widely dis- 
tributed in India west to the Caspian Sea, east throughout Burma, Indo-China, 
and the East Indies to New Guinea, and north through China to Manchuria; 
it also occurs in Japan, the Philippines, the Marianas, Hawaii, Madagascar, and 
Mauritius. Like A, (S.) aegypti it is being rapidly distributed by commerce. 
It can usually be recognized by the narrow median silvery-white stripe extend- 



MOSQUITOES 289 

ing nearly the whole length of the mesonotum, the white flat scales on the 
lobes of the scutellum, the broad white rings on all segments of the hind tarsi, 
and the white scales on the pleura of the thorax arranged in patches rather 
than in lines (Fig. 123). This species is largely dominant in its range and it can 
usually be recognized from the scutdlaris group by the white scales in patches 
instead of in broad lines on the pleura of the thorax. 5 A. albopictus is largely 
found about human habitations; it occurs up to 6000 feet in India and is re- 
ported breeding extensively in wooded areas in the lower mountain ranges of 
Hawaii. The adults are strongly anthropophilic and are persistent in their 
attacks. Though they usually bite outdoors during the twilight hours or in 
shady places during the day, yet the females readily enter buildings for a 
blood meal. This species breeds primarily in bamboo and tree stumps, tree 




Fig. 123. Left and center: Lateral and Dorsal views of the thorax of Aedes (Stegomyia) 
scutdlaris. Right: Lateral view of Aedes (S.) albopictus. 

holes, leaf axils, and coconut shells, and rarely in rock pools or artificial con- 
tainers. The breeding grounds are usually about human dwellings. Through- 
out its range it is an effective vector of dengue and it has been shown to be 
experimentally a vector of yellow fever. 

Aedes (Stegomyia) scutdlaris (Walker) [A. (S.) hebrideus Edw. is the 
same species] occurs in New Guinea, New Hebrides and probably on many 
other Pacific islands. Its breeding grounds are quite similar to those of albo- 
pictus though it also uses any available artificial containers. The adults are 
vicious biters and seem to prefer human blood. It is considered to be a vector 
of dengue (Daggy, 1944) anc ^ '** 1S reported to be naturally infected with 
Wuchereria bancrojti, 

Aedes (Stegomyia) simpsoni Theobald is an important semidomestic mos- 
quito. It breeds in tree holes, bamboo and leaf axils in banana plantations, and 



6 Unfortunately there are a number of species, usually not very abundant, similarly 
nlarked. These can only be identified by an examination of the male genitalia. 



290 MEDICAL ENTOMOLOGY 

similar situations. In northern Nigeria it was found to pass the dry season as 
eggs in its breeding places. In Uganda this mosquito is very common and 
yellow-fever virus was isolated from wild-caught specimens in 1941 (Smith- 
burn and Haddow, 1946); it is known to be an important vector. This mos- 
quito has a wide distribution in Africa from Gambia on the west to Abyssinia 
and south to the Transvaal wherever breeding conditions are favorable. Ac- 
cording to Haddow (1945), the female is almost exclusively diurnal in its 
biting habits. 

Aedes (Stegomyia) ajricanus Theobald is another species widely distributed 
in Africa and has recently been incriminated as a probable vector in main- 
taining yellow-fever virus among the native monkeys and possibly other 
animals. Smithburn and Haddow (1946) have shown this species to be the 
dominant arboreal form in Bwamba, Uganda, and it lives and feeds in the 
tree canopy. It attacks throughout the day, though the biting peak is during 
the early evening hours. 

Aedes sollicitans Walker is our famous salt-marsh or "New Jersey" mos- 
quito. It breeds in the great salt marshes from Maine to Florida and west to 
Texas along the Gulf shore, in the Antilles, Cuba, and Jamaica. The eggs are 
deposited in the moist marshes and they hatch when their breeding grounds 
are flooded by high tides or rains. Under favorable conditions the life cycle 
from egg to adult is only about ten days. Where conditions are favorable, 
breeding is continuous throughout the year; in the North the winter is passed 
in the egg stage. The females are vicious biters and frequently render life 
almost unendurable along the coastal areas. It also migrates considerable dis- 
tances; at least ^o-mile migrations are on record. Along the west coast from 
San Francisco south this species is replaced by Aedes squamiger, another 
troublesome salt-marsh breeder. In the interior Aedes dorsalis breeds in the 
saline, brackish, or alkaline pools found in the great plains. It also occurs in 
fresh water. It is one of the dominant species of the western plains of Canada 
and the United States. It has a wide distribution in North America, Europe, 
Asia, China, and is reported from North Africa. Aedes taeniorhynchus Wied. 
is another salt-marsh-breeding mosquito with an extensive range. It is reported 
as breeding along the coastal areas of North and South America, on the east 
reaching Connecticut and on the west Santa Barbara, California. It often 
occurs in enormous swarms, particularly in the southern portion of its range. 

In our northern woodlands we have a number of species that breed in vast 
numbers in spring pools formed by melting snows and spring rains. These 
species hibernate in the egg stage, and there is usually only one brood a year; 
the adults appear in early spring and live during the greater part of the sum- 



MOSQUITOES 291 

mer. The females are vicious biters, largely confining their attacks to those 
who invade their habitats, the woodlands. Here belong Aedes stimulant 
Walker, A. excrucians Walker, A. punctor Kirby, A. com munis de Geer, 
A. fitchii F. and Y., and others. Aedes vexans Meig. is one of the most wide- 
spread and annoying species of the genus. Next to Culex pipiens, C. fatigans, 
and Aedes aegypti, it is the most widely distributed mosquito species. It occurs 
practically throughout the Palearctic, Nearctic, and Oriental regions. It breeds 
primarily in fresh- water marshes, swamps, flooded river bottoms, meadow 
pools, etc., and often occurs in immense swarms after spring or early summer 
freshets. It is capable of rather extended migrations and may become a pest 
of the first importance. Normally it does not frequently invade houses though 
it may do so. It readily attacks man and other animals. There may be several 
broods a season, each following the flooding of their breeding grounds. (For 
further information on the species of this genus, consult the various refer- 
ences at the end of this chapter.) 

THE GENUS ERETMAPODITES: This genus deserves mention since 
Bauer (1928) demonstrated that E. chrysogaster Graham could act as a vector 
of yellow fever. It contains 18 species and 6 subspecies and all are restricted to 
Africa south of the Sahara Desert. One species occurs also in Madagascar. The 
larvae, as far as known, are predaceous and are found in leaf axils, fallen 
leaves, leafy pools, and snail shells in densely wooded or heavy vegetation 
areas and on banana plantations. The adults are active biters during the day 
in areas where larvae breed. Haddow (1946) states that they do not bite in 
the night or during twilight. As Africa is a reservoir of yellow fever, the 
importance of these mosquitoes in maintaining this reservoir' among animals 
may be of more importance than is now known. Haddow (1946) reports the 
isolation of a virus closely related to Rift Valley fever from a mixed group of 
these species collected in an uninhabited rain forest. 

THE GENUS HAEMAGOGUS: Haemagogus is close allied to Aedes 
though the species show many affinities to the sabethines. There are no very 
good characters to distinguish the genus, but their day-flying habits (nor- 
mally at high elevations) and their bright metallic blue and green colora- 
tion will aid in recognizing them. The species occur from Mexico to Argentina 
and are restricted to the New World. The species are very difficult to identify 
and as yet we have no thorough study of the genus as a whole. However, 
Kumm et al. (1946) have presented a detailed study of the species they found 
in Colombia. As far as known the species breed in tree holes, coconut shells, 
rock holes, bamboo joints, artificial containers, or similar situations, and the 



292 MEDICAL ENTOMOLOGY 

adults are normally active during the middle of the day and usually at rela- 
tively high elevations in the tropical forests. 

Haemogogus spegazzinii falco Kumm et al. is the most widely distributed 
species in Colombia, is regarded as an important vector of jungle yellow fever, 
has been found repeatedly naturally infected, and occurs abundantly in the 
jungle-fever areas. Furthermore it is the only species recorded by Kumm et al. 
(1946) with a hairy larva in Colombia. They further consider all references 
to H. capricornii 6 Lutz in this area to refer to the above species. H. janthinomys 
Dyar is also a synonym. Bates (1944) in an intensive study of H. capricornii 
( ? H. spegazzinii falco) in eastern Colombia confirmed the previous 
observations of Bugher et al. (1944) that this species is most active at high 
elevations (upper tree canopy) during midday and that its ground activity is 
increased by the cutting down of trees, thus increasing the light intensity of 
ground levels. This may explain the prevalence of jungle yellow fever among 
woodcutters. 

ANOPHELINE MOSQUITOES 

Anopheline mosquitoes are placed in at least three genera Chagasia, with 
three or possibly four species known only from South America and Panama; 
Eironella, with some six to eight species known only from New Guinea, the 
Solomons, and nearby islands; and Anopheles, which is world-wide in distribu- 
tion with nearly 400 species and varieties. The genus Anopheles has been 
divided into numerous genera, at least 38, but these are now regarded as 
synonyms though some of them are employed to indicate subgenera (Edwards, 
1932, recognizes only four subgenera). 

Anophelines can be distinguished from the culicines in all stages of their 
development. The eggs (Figs. 111,112) in all species are deposited singly or in 
small groups on the surface of the water and possess, in practically all species, 
lateral floats or air cushions. The larva (Fig. 106) does not possess a respiratory 
siphon and, when feeding, rests at the surface of the water and parallel to it 
(Fig. 124). The pupae can be recognized by the lateral spines (Fig. 104) 
being located at the lateral apical angles of the abdomen and normally are 
peglike except the last pair. The adults, both males and females in practically 
all species, have long palpi, usually as long as the proboscis (Fig. 125) ; the 
wings are usually spotted (Fig. 126) ; the scutellum is smoothly arcuate behind 



6 As all Haemagogus species can only be determined by the male genitalia or in most 
cases by larvae, it is interesting to note that no males of this species have ever been taken 
in the wild. Males were obtained by rearing from eggs obtained from captured females. 



MOSQUITOES 293 

with hairs evenly distributed, never distinctly trilobed with hairs and scales 
on the lobes except in the genus Chagasia. Furthermore the adults, when at 
rest, hold their bodies at a distinct angle, 30 to almost 90, while the culicines 
hold their bodies nearly parallel to the substratum (Fig. 127). 

The structure o the eggs of anophelines has already been described. How- 
ever, attention should be called to the recent studies of anopheline eggs and 




Fig. 124. Larva of Anopheles sp. resting and feeding at the surface of the water. Note 
the float hairs piercing the surface film and the thoracic lobe just behind the head attached 
to the surface film. 




Fig. 725. The heads of mosquitoes, (a) Male and female heads of a culicine mosquito. 
(b) Male and female heads of an anopheline mosquito. Ant, antennae; MxPlp, maxillary 
palpi; P, proboscises. ' ' 

their use in recognizing species. In the case of Anopheles maculipennis com- 
plex Bates (1940) recognizes five species and two varieties based largely on 
egg characters, though minute differences can be found in the adults, their 
activities (anthropophilic or zoophilic), their hibernation, their failure to 
make successful crosses in certain cases, and certain minute larval and male 
structures. Yet in this important malaria-transmitting complex the most reli- 
able characters for separating the species or races appear to be in the eggs. Cer- 
tain of these species are important transmitters of malaria (see pp. 306, 343). 
In Anopheles walf{eri the development of two egg types is a remarkable phe- 



294 



MEDICAL F.NTOMOLOGY 




Fig. 126. Wings of American Anopheles spp. (/) A. earlci. (2) 
A. quadrimaculatus. (3) A. wal^eri. (4) A. punctipennis. (5) A. cru- 
cians. (6) A. barberi. 



MOSQUITOES 295 

nomenon one type for summer breeding (Fig. 128) and a much larger, 
frost-resisting type (Fig. 128) for hibernation in the northern portion of its 
range. It is probable that some tropical species produce eggs that resist desicca- 
tion during the dry seasons (estivation) while the normal type is produced 
in the wet season. This seems to be indicated by the different illustrations of 
eggs of the same species by various authors. Unfortunately very little work 
has been done on this phase of mosquito biology. The eggs of most anophe- 
lines studied are not capable of withstanding much desiccation, a record of 




Fig. 127, The resting position of our common mosquitoes. Left; Culex pipicns. (All our 
common species except anophclines normally rest in this position.) Center: Anopheles 
quadrimaculatus. Right: A. crucians. 

about 15 days being the maximum. However, the study of the eggs for identi- 
fication purposes has shown interesting results. The work of Causey, Deane, 
and Deanc (1944) on the eggs of 30 South American species shows their wide 
variety and the variations within a single species. 

LARVAL HABITATS: It is not possible to generalize on larval habitats 
since many species would seem to have certain preferred breeding places 
though others readily accept any available aquatic situation suitable for larval 
development. In general, it may be said that anophelines rarely breed in open, 
wind-swept bodies of fresh water that are free of vegetation, along shore lines 
that are free of vegetation or debris, or in swift-running streams with clear 
margins, and not commonly in forest pools; a few species select saline pools 



2 9 6 



MEDICAL ENTOMOLOGY 



or marginal areas along the seashore, and some species select tree holes or 
water in epiphytic plants, as bromeliads. Anophelines occur in nearly all parts 
of the world except in the Arctic regions and at high mountain levels. In 
general it may be said that breeding occurs between the summer isotherm of 
60 North and between 60 and 70 of the southern summer isotherm. The 
A. maculipennis complex of the Old World has probably the most extensive 
distribution of any anopheline species. It occurs from Great Britain east 
through central Siberia to the maritime provinces and from Sweden and 
northern Russia south to North Africa and east along the northern portion of 
the Mediterranean through an extensive area of southern Russia to Mon- 
golia, Manchuria, and Japan. If the North American varieties (?) arc included, 




Fig. 128. Upper: The summer egg of Anopheles walfyri. Lower: 
Winter egg of die same species. 

it has a still wider distribution. This species also occurs at considerable eleva- 
tions. Its breeding grounds include fresh or brackish marshes, swamps, lagoons, 
rice fields, upland streams, cool fresh-water pools, ponds, and similar situations. 
The more common breeding places and distribution of the anopheline species 
which are known to be vectors of malaria are indicated in Table 7. 

Most anophelines occur in the lowlands. However, many species occur up 
to median elevations (1000 to 2000 feet) and some at considerable heights. In 
North America A, quadrimaculatus occurs commonly near Ithaca at over 1200 
feet; A. earlei has been taken at over 2000 feet; A. frecborni has been taken 
breeding at 7000 feet in Utah (Rees, 1943) ; 6000 feet in southern Idaho (Gjul- 



MOSQUITOES 297 

lin). In Mexico A. parapunctipennis and A. pseudopunctipennis occur com- 
monly from 3000 to 6500 feet. In the Andean region Hackett (1945) reports A. 
pseudopunctipennis breeding at elevations of 2773 meters (about 8550 feet) ; it 
is the primary vector of malaria throughout the mountain region at elevations 
of from 250 to 2500 meters. A. eiseni has been taken up to 5000 feet. A. argyri- 
tarsis occurs from the lowlands to at least 5000 feet, and in Guatemala it 
abounds at 2000 feet. In Mexico A. albimanus occurs in the rainy season from 
the lowlands to over 3000 feet. In Venezuela Anduze (1943) reports A. strodei 
and A. oswaldoi as breeding up to 1600 feet, and A. argyritarsis, A. eiseni, A. 
neomaculipalpus, and A. pseudopunctipennis were taken up to 3300 feet. Be- 
tween 3300 and 8200 feet A. argyritarsis, A. pseudopunctipennis, and A. boli- 
viensis were found breeding. In Mexico A. pseudopunctipennis occurs from 
sea level to 7200 feet or more, while Shannon reports it in the Andes at 7800 feet. 

In Africa A. garnhami occurs in the Kenya mountains to as high as n,ooo 
feet; A. implexus occurs from 3000 to 5000 feet, breeding in deep forest shade 
in swamps, springs, and seepages; A. fyngi is reported breeding at 7000 feet; 
A. gambiae breeds from sea level to 7000 feet in Abyssinia, at 5100 feet in 
Arabia, and at 4000 feet in Uganda. 

In India a long scries of anophelines are reported breeding from 2000 to 
11,000 feet. Christophers (1933) records the following species: A. aitk^eni, 
A. moghulensis, and A. jeyporicnsis are found from the plains to at least 
6000 feet; A. hyrcanus nigerrimus, A. turJjJiudi, A. annularis, and A. annan- 
dalei go as high as 7000 feet; A. maculatiis willmori occurs in the foothills of 
the Himalayas from 2000 to 8000 feet; A. culicifacies is reported even as high as 
7500 feet; A gigas gigas usually occurs from 5000 to 6000 feet in southern India, 
while A. gigas bailey i has been taken at 11,000 feet in Tibet; A. barianensis, 
a tree-hole breeder, occurs from 5000 to Hooo feet in the northwest Himalaya 
region; A. minimus breeds abundantly at 2000 feet and occurs to at least 5000 
feet; A. fhwiatilis, a stream breeding species, occurs at elevations between 
1000 and 7500 feet. Other species might be added to this brief list. 

In the Australasian region A. minimus occurs from sea level to 3000 feet; 
A. farauti has been reported to as high as 2000 feet; and A. stigmaticus occurs to 
elevations of as much as 6000 feet. 

THE ADULTS : It is not possible to give a general summary of the biology 
of the adults. Instead a brief summary of the biology of a few of the more 
important vectors of malaria with a discussion of the adults must suffice. 

Anopheles quadrimaculatus (Say) (Fig. 129) is the most important vector 
of malaria in North America. Its distribution extends from New Hampshire 



298 MEDICAL ENTOMOLOGY 

and Massachusetts west through central New York and southern Ontario to 
Minnesota and Iowa, south throughout the southern states, and west to 
central Texas, Oklahoma, and eastern Kansas. It also occurs in eastern Mexico 
south to Veracruz. The adults are active during the evening, night, and 
morning hours and readily enter houses or other buildings in search of blood. 
They readily feed on man and wild and domestic animals. Normally they do 




Fig. 729. Two of our common anophelincs. Lcjt: Anopheles pttnctipcnnis. Right: 
A. quadrimaculatus. 

not feed during the daytime, though they will attack in houses and out of 
doors during dark and cloudy weather. During the day they may be found 
resting in dark corners in buildings, underneath all kinds of houses, in stables 
and hollow trees, under bridges and culverts, in outdoor privies (one of the 
most common places), and in any shelter that provides darkness and moisture. 
The males and females mate shortly after emergence either after or before a 
blood meal. Keener (1945) describes the mating in small rearing cages as tak- 
ing place about 8 P.M. They mate in flight, then usually fall to the bottom of the 
cage and separate after about 10 to 15 seconds (stenogamous species). A single 



MOSQUITOES 299 

mating is sufficient to ensure fertile eggs during the life of the female. If blood 
meals are available oviposition takes place about three days after emergence. 
Keener records each female as laying 9 to 12 batches during its lifetime; each 
batch varied from 194 to 263 eggs. Three hundred females deposited 200,000 
eggs during their life or an average of 660 eggs per female. Well-fed females ap- 
parently may lay from 2000 to 3000 eggs. Oviposition occurred during evening 
hours. The length of life of the female varied from 7 to 62 days, with a mean 
of 21 days; the males varied from a few days with a mean of 7 days. How long 
they may live in nature is not well known. 

The breeding places are most commonly ponds, pools, grassy and weedy 
margins of lakes, swamps, and collections of water with floating debris or 
emergent or floating vegetation. It seems to prefer open, sunlit waters with 
debris or vegetation, though it breeds in water areas densely shaded by tall 
trees. During the summer season the larval period is comparatively short. The 
eggs hatch in from 2 to 3 days and the larvae complete their growth in from 
12 to 19 days, depending on food supply and water temperature. The pupal 
period varies from 2 to 6 days. Hurlbut (1943) found the average period from 
egg to adult to vary from 18 to 23 days at an outdoor temperature of about 
74 F. The number of generations per season varies according to the region 
studied. Boyd (1930) concluded there were seven to eight annual generations 
in North Carolina, and in southwestern Georgia eight to ten. Hurlbut (1943) 
records nine to ten generations in northern Alabama. Bradley and Fritz 
(1945) present an interesting account, based on extensive data, of the duration 
of the significant breeding season in each of the annual isothermal zones 
at 5 F. intervals (50 to 55, 55 to 60, 60 to 65, 65 to 70, and 70 to 
75 F.) in the United States, and within each zone the average annual 
temperature varies only within 5 F. In the 70 to 75 isothermal zone breed- 
ing is continuous throughout the year, but in the 50 to 55 isothermal zone 
breeding occurs only from late May to the middle of October. In the north- 
ern portion of its range and at high elevations the females (the males die 
off) seek hibernating quarters in cool, dark places such as cellars, hollow 
trees, caves, and r'tnilar locations where there is a certain amount of mois- 
ture. In the warmer portions of its range true hibernation is regarded as 
doubtful since breeding n:ay be continuous, and larvae have been taken in 
practically every month of the year. It is probable that in the cool season larvae 
succeed in withstanding considerable cold weather and that the larval de- 
velopment period is greatly lengthened, thus providing for rapid production 
at the beginning of warmer weather. 
' Anopheles jreeborni Aitken (A. maculiiennis jrceborni Aitken) is widely 



300 MEDICAL ENTOMOLOGY 

distributed in North America west of the Rocky Mountains and extends 
from southern British Columbia south through western Montana, Utah, 
Colorado, and New Mexico to western Texas. Within this area its breeding 
grounds are restricted by more or less local conditions. In California it is 
widely distributed except along the north coast and is very abundant in the 
San Joaquin and Sacramento Valleys. In southern California it reaches the 
coast at San Luis Obispo. It is abundant in the Willamette Valley, Oregon, 
and Stage reports it breeding in abundance in irrigated hayfields in the arid 




Fig. 130. Photograph of a ro,ooo-acre irrigated hayfield in eastern Oregon. Note the low 
section in the left-hand corner with weeds and water. Here breed Anopheles jrecborni, 
Aedes flavcscens, A. dorsalis, and Culex tarsalis. (Courtesy Mr. Stage, U.S. Bureau of 
Entomology and Plant Quarantine.) 

section of eastern Oregon (Fig. 130). Rees (1943) indicates a wide distribu- 
tion in Utah. He reports taking this species at an elevation of 7000 feet. 
According to Freeborn (1943), the breeding grounds are mainly small, in- 
significant fresh-water pools that are at least partially CAposed to sunlight 
and where there is vegetative protection such as algae. Such places include 
hoofprints in seepage areas, small bays in streams, cutofT pools, roadside 
pools, and semipermanent pools in irrigation areas. It rarely breeds in foul 
water, artificial containers, or large bodies of water such as ponds or borrow 
pits or in swamps or wooded areas. Hardman (1947) has reared this species 
under artificial conditions and produced seven generations in seven months. 



MOSQUITOES 301 

He found maximum egg production in a wild-caught female to be 1527 
whereas laboratory-reared females averaged 751. 

The adults closely resemble A. quadrimaculatus but they can usually be 
separated by the markings of the mesonotum. In jreeborni there is a rather 
distinct median, longitudinal, pruinose stripe, whereas in quadrimaculatus 
the mesonotum is uniformly dark without any indication of a median stripe. 
The larva of jreeborni is practically identical with that of punctipennis. 
According to all recent workers, jreeborni is the prime vector of malaria 
within its range. It is known to seek human blood, readily invades houses, 
and is a vicious indoor biter. 

Anopheles occidcntalis Dyar and Knab (A. maculipennis occidentalis and 
A. maculipennis of authors 7 ) is apparently restricted to a coastal area 
stretching from Ventura Bay north to Washington and British Columbia. 
It has also been collected in Alaska and the Yukon, and Aitken reports it 
from Aklavik on the Mackenzie River at 69 North latitude. The eastern 
form listed under the above name is undoubtedly a distinct species and is 
described as A. earlei Vargas. Both species have the distinctive coppery or 
golden spot at the apex of the wing. Aitken (1945) does not give much 
information on the biology of this species, but apparently it is not abundant 
in its range and plays no part in the transmission of malaria. He does not re- 
port it as a house invader. 

Anopheles earlei Vargas is a species based on the study of females from 
Wisconsin; the type male came from Cayuta Lake, New York. Here (eleva- 
tion 1272 feet) it usually occurs in abundance, though its larval habitats have 
not been studied intensively. However, it can be separated in all stages from 
A. occidentalis as described by Aitken (1945). The females bite readily during 
the daytime but attack most vigorously during the twilight hours (till 9 P.M. 
at least). It readily invades houses and the females enter hibernation in 
situations similar to those of A. quadrimaculatus. Its distribution is not well 
known, though probably it is the species that extends from Maine south to 
New York and west along the United States and Canadian borders to the 
Rocky Mountains. It is definitely known from New York, Michigan, and 
Wisconsin. Preliminary experiments by Dr. Boyd indicate that this anophe- 
line may be a vector of malaria. 

Anopheles psettdopunctipennis Theobald is apparently a variable species 



7 Aitken (1945) gives a detailed synonymic statement of this species, but his references 
to this species east of Wisconsin and Michigan and probably cast of the Rocky Mountains 
do not refer to this species. See A. earlei Vargas below. 



302 MEDICAL ENTOMOLOGY 

and may consist of several species or subspecies. The adults may be dis- 
tinguished from closely related North American species by the whitish areas 
or spots (usually 2) on the costal margin of the wing, the fringe with pale 
spots at tips of veins, and terminal segment of the female palpus white. 
A. franciscanus, regarded by Aitken as a subspecies or variety, may be sep- 
arated by the terminal segment of the female palpus not being entirely white 
but with an apical black ring. In the larval stage the presence of "tails" on 
the postspiracular plates of the respiratory apparatus is diagnostic through- 
out its range except in many parts of California where the "tails" are lacking. 
This anopheline (or its varieties) is probably the most widely distributed 
species in the Americas and occurs from about 42 North latitude in the 
western part of the United States through Mexico, Central America, Panama, 
Colombia, Venezuela, and south to northeastern Argentina (Cordoba, 31 
South) and Chile (Pica, 20 30') following the foothills on both sides of 
the Andes. It also occurs in Trinidad and Grenada. According to Aitken 
(1945), this species prefers arid canyons and valleys where the larvae occur 
in the small, clear, slow-moving streams and side pools of receding rivers 
containing a rich growth of algae and exposed to the sun. Barber reports it 
breeding also in cool pools in the shade in New Mexico. In Mexico it com- 
monly occurs in shaded pools with algae. Its preference seems to be in more 
or less exposed waters with abundance of algal growth. According to Recs 
(1943) the females hibernate, and he found them commonly in outbuildings 
and human dwellings in southern Utah. The relation of this variable species 
to malaria is discussed on pages 341-343. 

Anopheles punctipcnnis (Say) (Fig. 129) is the most widespread anopheline 
in North America. It ranges from southern Canada south to the Gulf of Mexico 
and reaches the Mexican plateau (state of Hidalgo); west of the Rocky 
Mountains it ranges from British Columbia south through Washington and 
Oregon to southern California; it is rare or not found in most of the moun- 
tain states. In the east its breeding places are varied rain-water barrels, 
roadside puddles, ruts in muddy roads, grassy bogs, swamps, hog wallows, 
spring pools, margins of streams, lakes, and open ponds. The writer has re- 
cently taken it in deep woodland pools (October, 1945). The adult females 
hibernate in cellars, houses, outbuildings, and similar situations. Frequently 
during the winter they will invade sleeping rooms and bite. The females 
usually attack during the twilight hours and when abundant readily enter 
houses and seek blood. 

Anopheles crucians Wied., A. bradleyi King, and A, georgianus King con- 
stitute a complex that presents many difficulties. A. crucians occurs from 



MOSQUITOES 303 

Massachusetts south through the eastern states to the Gulf of Mexico and 
west to western Texas and north to Illinois and Kentucky. It breeds almost 
exclusively in acid waters. A. bradleyi ranges along the Atlantic coast from 
New Jersey to Veracruz, Mexico. It normally breeds in saline pools. A. 
gcorgianus has been taken in Georgia, Alabama, and Louisiana and breeds 
in fresh water. Though these species, at least crucians, readily bite humans, 
they are not considered of any importance as vectors of malaria. Sabrosky 
et al. (1946) report 3.38 per cent infection in November with Plasmodia in 
South Carolina, and these species may play a more important role than is 
now recognized. 

Anopheles wal\eri Theobald is widely distributed in the eastern half of 
the United States west to Minnesota and western Louisiana. It is a fierce biter, 
attacking principally during twilight hours. If disturbed it will attack during 
the day. It is attracted to lights and is frequently taken in numbers at light 
traps. It is the only known anopheline that hibernates in the egg state in the 
northern part of its range. 

Anopheles atropos Dyar and Knab is a salt-water breeder and occurs along 
the Atlantic coastal area from New Jersey to Texas and is reported from 
Cuba. Anopheles barberi Coquillett breeds in tree holes (Fig. 119) and is our 
only North American anopheline that hibernates as young larvae frozen in 
the water. It is a very small species. It is widely distributed in the eastern 
half of the United States north to Iowa and New York. It has been shown 
capable of infection with Plasmodium vivax and did transmit the infection 
from the sick to the well (Stratman, Thomas, and Baker, 1936). 

The subgenus Nyssorhynchus is restricted to a region extending from 
Mexico, through Central America, to South America and most of the West 
Indies. Only a single species, A. (N.) albimanus Wied., occurs in the United 
States, and it is known only from a small area in southeastern Texas around 
Brownsville and in southern Florida. These are frequently called the "white- 
footed" anophelines because the last three segments of the hind tarsi are 
nearly all white. Lane (1939) lists 17 species in this subgenus from the neo- 
tropical region but today the total is probably greater. Causey, Deane, and 
Deane (1946) recognize IT species composing the tarsimaculatus complex 
in northeast Brazil. This would give us over 25 recognized species. In this 
group the male gcnitalia is characteristic only one basal spine on a tubercle 
on the sidepiece with two other spines inserted near the middle. The larvae 
do not seem to be characterized as a group or easily separated from the sub- 
genus Anopheles. In this group arc many important vectors of malaria. These 
include A. albimanus, A. darlingi, A. albitarsus, and A. aquasalls. 



304 MEDICAL ENTOMOLOGY 

Anopheles (Nyssorhynchus) albimanus Wied. has a wide (distribution in 
Mexico, Central America, Panama, the West Indies, Colombia, Ecuador, and 
Venezuela and also occurs in Texas and Florida. The adults are persistent in- 
vaders of dwellings and are avid feeders on man, though they attack horses 
and other animals. They are primarily nocturnal and definite flights are re- 
corded in Panama. These flights occur in the early evening hours and usually 
last 30 to 45 minutes. During the night the mosquitoes remain in houses but 
leave in the early morning hours for other shelter (the writer has seen adults 
1 7] taken in a native Mexican hut full of blood about n A.M'.). Collection 
of this species while it is resting during the day in native huts is common in 
the state of Veracruz (Mexico). Extensive migration of this species has been 
recorded and flights of 12 miles or more have been noted in Panama. The 
principal requirements for breeding places are sun, vegetation, and little or 
no movement of water. It breeds extensively in clear pools, slow and stagnant 
streams, tracks in pastures, open ponds, swamps, seepage areas, potholes, 
ditches, road ruts, and lakes with surface vegetation; it also breeds in brackish 
pools open to sunlight. Normally this species is restricted to the lowlands 
throughout its range, though in the rainy reason it breeds abundantly at over 
3000 feet in Veracruz. It is one of the important vectors of malaria. 

Anopheles (N.) darlmgi Root was described from the state of Rio de Janeiro 
in 1926 and is known as an excellent vector of malaria. Its distribution is 
from Argentina to Venezuela; it also occurs in British Honduras and Guate- 
mala. Recently (1943) it has been found in the state of Chiapas, Mexico, and 
more recently (1946) in th_ state of Tabasco. It undoubtedly will spread along 
the coast line of the Gulf of Mexico and should easily gain access to the 
southern United States. Its favorite larval habitats are among mats of vege- 
tation in shaded, clear, fresh water of lagoons, overflows, and floodwaters as 
in the Amazon Valley. According to Shannon (1933), tms species is primarily 
a lowland breeder and is associated with flood water conditions. The adults 
are consistent invaders of houses and prefer human blood. Bates (1947) and 
Sigioli (1947) report that this species breeds readily under artificial conditions. 

Anopheles (N.) aqttasalis was described by Curry (1923), who separated it 
from the so-called tarsimaculatus complex. It is a brackish water breeder and 
appears to be quite restricted to shaded or open brackish tidal swamps, 
especially along tidal river areas, on the Atlantic side of Panama, Nicaragua, 
Trinidad, the lesser Antilles, and as far south as Pernambuco and Algoas in 
Brazil. It is also recorded breeding inland (TO miles) in the rice fields of 
Trinidad. The adults feed freely on animals and man and readily enter 



MOSQUITOES 305 

houses. However they leave their feeding grounds before dawn and are rarely 
found in buildings during the day. Throughout its range it is an important 
vector of malaria. 

Anopheles (Kcrteszid) bellator Dyar and Knab is an interesting anophe- 
line as its only known breeding places are the contained water in epiphytic 
bromcliads. It occurs in Trinidad and Venezuela. In Trinidad this mosquito 
breeds abundantly in the water collected in bromcliads on the immortelle 
(Erythrina), which is used as a shade in the cocoa plantations, and on other 
trees on the highlands. The adults are anthropophilic, attacking humans dur- 
ing the evening hours (5 to 8 P.M.) ; they seek human habitations but leave 
immediately after feeding; they also feed in the early morning hours. The 
observations of de Vertcuil (1925-1937) that this anopheline, on epidemio- 
logical evidence, is an important vector of malaria in Trinidad have been 
abundantly confirmed by Rozeboom and Laird (1942) and Downs, Gillette, 
and Shannon (1943). 

Anopheles gambiac Giles is probably one of the most effective transmitters 
of malaria in regions where it and malaria are present. It occurs over most 
of tropical and subtropical Africa where breeding conditions are favorable 
from the Sahara Desert south to Natal. On the eastern side of Africa it is 
abundant in Ethiopia and Eritrea and occurs north to Khartoum and southern 
Egypt. It occurs in Arabia and the islands of Mauritius, Reunion, and Mada- 
gascar. This anopheline is primarily a small pool breeder, frequenting such 
places as puddles, shallow ponds, animal footprints, roadside ditches, irriga- 
tion furrows, pools in beds of drying streams, and similar locations. Sunlight 
appears to be favorable to larval development, and the absence of vegetation 
and open shallow water are preferred. It is rarely taken in artificial containers. 
In Brazil where it gained a foothold (now exterminated) in 1930 the pre- 
ferred breeding places were in "small, shallow, sunlit pools of fresh water 
without vegetation" and in the neighborhood of human habitations. Though 
the above statement is in accord with investigations in many parts of Africa 
and Brazil, yet Haddow et at. (1947) report this species as the most abundant 
in a tropical rain forest far from human habitation in Bwamba County, 
Uganda. They took it in the center of the forest and at all elevations from 
the ground to the tree canopy (82 feet) during both the dry and rainy sea- 
sons. Out of a total of 32,315 mosquitoes taken, 30,240 were A. gambiae. 
These captures represent 24 hours of collecting at all levels for 20 days each 
during 1944 and 1945 in both dry and rainy seasons. (In all 40 collections 
from both dry and rainy seasons were made in these two years; the elevation 



3 o6 MEDICAL ENTOMOLOGY 

stations were at o, 16, 31, and 54 feet during the rainy season of 1944 an ^ tne 
dry season of 1945 at Mongiro; elevations of o, 22, 44, 58, and 82 feet were 
employed during the rainy season of 1944 and the dry season of 1945 at 
Mamirimiri.) 

The Anopheles maculipennis complex of Europe and Asia has been studied 
more intensively than any other anophcline group. Formerly the group was 
considered a single species with a wide distribution extending from England 
and Sweden across Russia to Japan and south to coastal areas of northwest 
Africa and thence cast along the northern Mediterranean lands east through 
parts of Russia to Mongolia. As this species was a good vector of malaria, it 
became apparent that malaria, even in the centers where it should occur, 



Hi Hi HJ Bd 3 As Md 



Pad Pa 




Fig. 1^1. Wing of Anopheles gambiac, illustrating the costal wing spots. Pale spofs: 
A, apical spot; As, accessory sector spot; Hi, H 2 , II 3 , humeral spots; Pa, prcapical spot; 
S, sectoral spot; Sc, subcostal spot. Dark, spots: Ad, apical dark spot; Bd, basal dark spot; 
Md, median dark spot; Pad, preapical dark spot; Sq, the squama. 

was absent despite the abundance of this species. Furthermore, it was demon- 
strated that in some areas the females avoided man and preferred animal 
hosts (i.e., were zoophilic). The differentiation of the varieties of this com- 
plex has involved prolonged studies, and even today the only satisfactory 
characters are found in the eggs. As a result this complex has been divided 
into a number of species and subspecies which, even at present, are not well 
understood. The latest summary of Bates (1940) lists five species and two 
subspecies. These are A. maculipennis Meig., the typical form widely dis- 
tributed in Europe and probably Asia; A. messae Falleroni, closely associated 
with A. maculipennis and with a similar range; A. melanoon melanoon 
Hackett, said to be restricted to the Italian peninsula; A. melanoon subalpinus 
Hackett and Lewis, occurs in Spain, northern Italy, and the Balkans; A. 
labranchiae labranchiae Falleroni, said to be restricted to Spain, Italy, certain 
Mediterranean islands, and North Africa; A. labranchiae atroparvus van 
Thiel, which is widely distributed in central Europe and Asia; and A. sacha- 



MOSQUITOES 307 

rovi Favr, which is widely distributed in the Mediterranean area east to cen- 
tral Russia and beyond. The biology and the relation of these forms to the 
transmission of malaria have been fully presented by Hackett and Missiroli 
(1935) and Hackett (1937). 

The subgenus Myzomyia Blanchard is known only from the Ethiopian, 
Oriental, and Australasian regions. The main differentiating character for 
this group is in the male genitaiia. The sidepicce lacks an internal spine and 
the basal spines number four to six and are not set on tubercles. The wings 
arc nearly always spotted with four pale spots on the costal margin. In the 
larvae the only character of value is the antennal hair ($rn); it is always 
simple. Here belong a large number of species of which a considerable num- 
ber are important vectors of malaria. These include A. (M.) [unestus Giles 
(important vector in tropical Africa and Mauritius; A. (M.) gambiae Giles 
(see above) ; A. (M.) hargreavesi Evans (vector in Sierra Leone, Nigeria, 
Belgian Congo, etc.); A. (M.) moitchete Evans (vector in central Africa); 
A. (M.) pharoensis Thco. (vector in Africa including Egypt, Palestine); A. 
(M.) nili Thco. (vector in many parts of Africa) ; A. (M.) pretoriensis Theo. 
(probable vector when abundant in Africa) and many others as may be seen 
in Table 7 (pp. 342-347). 

DISPERSION AND FLIGHT 

"Dispersion" may be differentiated from general "flight" and defined as the 
ordinary distance mosquitoes travel from their place of breeding to a readily 
available blood source within a comparatively short distance. "Flight" may 
be assigned to the conditions when mosquitoes breeding in certain areas have 
to search for blood at considerable distances such as nearly a mile or more. 
When food is readily available there may be no need for extended flight; 
when food is scarce and maximum production of adults occurs, then the 
adults must go far afield. 

Dispersion is undoubtedly the most important question from the standpoint 
of the epidemiology of the diseases transmitted by mosquitoes, though ex- 
tended flight must always be taken into account when mass production of 
any species occurs. In general, it has been fairly well established that a mile 
zone about the breeding grounds of anophclines is their normal range. 
However, many factors may intervene to extend this zone, and then we may 
speak of the "flight" of anophelincs or of their distribution. Some of these 
factors are: (i) mass production in any area in which a blood source is not 
sufficient to meet the needs of the adults; (2) favoring winds that aid in a 



3 o8 MEDICAL ENTOMOLOGY 

wider distribution; and (3) artificial means of distribution that may carry 
them far beyond any normal flight range. During the past years many ex- 
periments have been conducted by mass liberation at central points of 
anophelines marked by means of aqueous aniline dyes or colored powders 
such as bronzing, gold, or aluminum powders, etc. After liberation the prob- 
lem of capture of the marked specimens involves tedious labors and requires 
a large number of collecting points around the periphery. However, many 
such experiments have been conducted. Only a brief summary of flight range 
can be presented here. 

FLIGHT RANGE OF ANOPHELINES 

Anopheles quadrimaculatus Say has been experimented with by many 
workers. It seems now fairly well established that a mile zone about its breed- 
ing places is the normal, effective dispersal area. However, adults have been 
taken at 2 to 2.5 miles (3200 to 4000 meters) from the center of liberation 
(Eyles and Bishop, 1943). Eyles et al. (1945) report good dispersal at 2.7 miles 
and further flights to 3.63 miles, and Gartrell and Orgain (1946) found at 
Kentucky Reservoir a good 3-mile flight during mass breeding. HufTaker 
and Back (1945) report similar conditions in Delaware, where mass produc- 
tion occurred over an extensive area (1500 acres of breeding area) and despite 
abundance of blood supply the females easily migrated to the i-milc (250 
9 9 per shed) and to the i. 5-mile (10 9 9 per shed) zones. They also 
report taking females at 3 miles from the breeding zones. Clarke (1943) 
stained masses of emerging mosquitoes and recovered this species 8 miles 
distant on the second day and A. pitnctipennis 10.5 miles distant on the 
seventh day. These studies indicate the maximum ranges recorded for this 
species, though all workers agree that the effective flight range is a mile or 
less. 

Anopheles crucians Wicd. is on record for rather long sustained flights. 
Metz (1918) noted flights of nearly 2 miles. Barber et al. (1924) records ex- 
tensive flights into Gulfport, Mississippi, from offshore islands where breed- 
ing was intensive and no mosquitoes could be found breeding on the coast; 
the distance varied from 3 to 12 miles. McCreary and Stearns (1937) cap- 
tured adults at lighthouses in Delaware Bay at 3.2 and 5.5 miles distant from 
the nearest shore line. 

Anopheles freeborni Aitken was noted by Freeborn (1921, 1932) to under- 
take long migratory flights when emerging from hibernation. The extent 
was not given but a flight of nearly 4 miles was implied. However there 



MOSQUITOES 309 

does not seem to be any very definite data on the ordinary dispersal flights 
during summer breeding. 

Anopheles albimanus Wied. has rather extensive flight records. Normally 
most of the workers stress the usual flight as % to i mile. These flights occur 
at dusk and dawn and usually last for 30 to 45 minutes, the dusk flight in 
search of food and the dawn flight a return to the resting places. However, 
this species will remain in houses during the day. When mass breeding 
occurs as on Gatun Lake when it is overgrown with Naja and other aquatic 
vegetation, flights of 12 miles are noted and along with these migrations to 
the sanitated areas a rise in the malaria rates. 

Anopheles gambiae Giles has a flight range of normally % to i mile, though 
experiments in various parts of Africa show a maximum range of 4.25 miles 
down wind and 1.5 miles against wind (Adams, 1940). Hacldow et al. (1947) 
found this mosquito the most abundant species in a forested area in Uganda, 
and it was taken at all flight stations from the ground up to 82 feet in the 
forest canopy. This would certainly indicate that tinder favorable conditions 
this species could migrate long distances. However, in the eradication of this 
species in northeast Brazil every indication points to localized spread: distant 
points become infested as the result of various means of carriage. Furthermore, 
it was found to be almost completely restricted to places surrounding human 
habitation and never reported from forested areas. In other words it was a 
house-frequenting, anthropophilic mosquito. 

Anopheles maciilipennis complex presents a more complicated problem in 
determining range of dispersion or flight. Extensive flight studies in various 
parts of Europe by means of released, stained mosquitoes clearly show a flight 
range of several miles (^ to 4 miles), but which species of this complex is not 
clearly indicated. In Holland Swellengrebel and Nykamp (1934) found a 
maximum range of 5.7 to 8.7 miles of marked mosquitoes ( 3 and ? ) from 
their breeding grounds. Shipova (1936) released 1253 stained adults in October 
and recovered 52 stained individuals in hibernating quarters at 2, 6, 9, and 
11.25 mil cs from the point of release. Many other experiments could be cited 
but it seems fairly well established that the normal dispersion is usually 
within the i- to 2-mile etlective range, though longer flights are common and 
must be taken into consideration when developing effective control measures. 
A. sacharovi Favr, a closely related species, has a recorded range of 2.8 miles 
(Kligler, 1924) and a maximum seasonal flight of 8.71 miles (Kligler and 
Mer, 1930). 

The flight range of a considerable number of anophelines, particularly 
those known to transmit malaria, has been investigated. A. maculatus Theo., 



3 io MEDICAL ENTOMOLOGY 

though usually given as rarely dispersing more than a half-mile in Malaya, 
has been shown by Wallace (1940) and Strahan (1941) to exceed even a mile 
flight and is an important agent in maintaining malaria to much more than 
the half-mile zone. Anopheles minimus Theo. seems to be restricted to about 
a half-mile dispersion though longer flights have been recorded (8 miles; 
Manson and Ramsay, 1933), but such flights do not seem to have been sub- 
stantiated by other workers. A. minimus flavirostris (Ludlow), an important 
vector of malaria in the Philippines, was shown by Russell and Santiago 
(1934) to remain rather close to its breeding grounds, rarely exceeding a 
mile, though previous epidemiological evidence (Craig, 1909) indicated a 
much greater flight range. The following species appear to be largely re- 
stricted to the half-mile or mite zone : A. aconitus Donitz, A. argyritarsis R.-D., 
A. culicifacies Giles, A. fluviatilis Giles; the following to a range of over i 
mile: A. junestus Giles, A. multicolor Camboulin (max. 8 miles), A. sacha- 
rovi Favr, A. pseudopunctipennis Theo., A. sergcnti Thco., A. stephensi 
Liston, A. sundaicus (Rodenwalclt), A. siipcrpictus Grassi, and A. walf^eri 
Theo. (1.5 to 2 miles). 

FLIGHT RANGE OF CULICINES 

The dispersion of culicines has not received the same attention as that of 
anophelines. The following brief notes may be of interest. 

Culex pipiens Linn, has been taken at least 14 miles from where the mos- 
quitoes were dusted with aniline dyes (Clarke, 1943) during a period of 47 
days, the average flight range being 9.2 miles. McCreary and Stearns (1937) 
captured a male and females (12) by light traps 8.2 and 8.4 miles from the 
nearest shore line. Employing marked specimens Afridi et al. (1938) reported 
Culex fatigans Wicd. infiltrating into the urban areas of Delhi for at least 3 
miles. Culex apicalis Adams, C. salinarius Coq., and C. restuans Thco. have 
been taken at light traps at 8.2, 8.4, and 3.2 miles respectively from the nearest 
shore line (McCreary and Stearns, 1937). 

Aedes aegypti (Linn.) has apparently a narrow range of dispersal. Shan- 
non and Davis (1930) in extensive experiments in Brazil demonstrated a sus- 
tained flight over open water of 1000 meters by employing stained specimens. 
Its dispersal on land is known to exceed 500 yards, but in general its move- 
ments are rather closely restricted to human habitations where it migrates 
from house to house and its nearby breeding grounds from day to day. 

Aedes albopictus (Skuse), like A. aegypti, has a restricted range of move- 
ment. Bonnet and Worcester (1946) in a series of well-planned experiments in 



MOSQUITOES 311 

Hawaii with marked individuals concluded that the dispersal range rarely ex- 
ceeds 200 yards during the lifetime of the adults. Aedes sollicitans (Walker) is 
known to migrate considerable distances by mass flights, at least 30 to 40 miles. 
Curry (1939) recorded an invasion of a ship no miles distant from Cape 
Henry, North Carolina, by a swarm that caused considerable annoyance to the 
passengers. In Delaware McCreary and Stearns (1937) collected large num- 
bers of males and females at light traps placed 8.2 and 8.4 miles from the 
shore line. In the same traps Aedes cantator (Coq.) were also taken. Though 
these two species breed primarily along our tidal marshes, yet they have been 
taken in many of the salt pools located inland as at Ithaca and Syracuse, New 
York, and at various points inland in Alabama, Florida, Georgia, North and 
South Carolina, and Mississippi. Aedes squamigcr (Coq.) a salt-marsh 
breeder along the southern half of the California coast line is stated by Herms 
and Gray to migrate as much as 50 miles. Aedes taeniorhynchus (Wied.), 
another salt-marsh breeder, is known to migrate considerable distances, 
though verified flights do not exceed eight or nine miles (McCreary and 
Stearns, 1937). Like A. sollicitans it has been found breeding in salt pools far 
inland (30 to 240 miles) but this is certainly not an invasion by sustained 
flight. Probably the most extended flights of salt-marsh breeders are by Aedes 
vigilax Skuse, for which Hamlyn-Harris (1933) reports 6o-mile migrations in 
Australia, and Aedes (Mucidus) alternans Westw. 8o-mile migrations. 

Among fresh-water-breeding mosquitoes there are a number of interest. 
Aedes vexans Meig. has many records of 5-, 10-, and even 20-mile migrations 
from known breeding grounds, and in many cases the migratory flights have 
been followed day by day from breeding grounds for at least 5 miles. Aedes 
latcralis (Mcig.), a serious pest in British Columbia, Washington, and Oregon, 
is known to migrate at least 10 to 30 miles. Stained specimens were actually 
taken 5 miles from the point of liberation, and the species was abundant 15 
miles from its breeding grounds but gradually diminished at the 25-mile 
limit: one was taken 30 miles from breeding grounds (Stage, 1938). Aedes 
dorsalis (Meig.) and Aedes spencerii (Theo.) are reported as -migrating 
several miles but no experimental data are available. One female of the latter 
species was taken at Lake Placid, New York, on July 26, 1945, over at least 
500 miles from its known eastern range. 

The problem of mosquito dispersion by air currents or flight to the upper 
reaches of the atmosphere presents another phase. It is now well known that 
a number of mosquitoes frequent the upper canopy in many tropical forests. 
The work of Glick (1939) demonstrated that mosquitoes may be collected 
at quite high levels both day and night during their breeding season. In all, 



3 i2 MEDICAL ENTOMOLOGY 

in specimens of mosquitoes were taken in airplane flights throughout the 
five years, representing seven genera and six determined species. Of these, 
44 were taken in the daytime and 67 at night. The night flying was only 
10 per cent of the total time in the air. Anopheles quadrimaculatits was taken 
both day (3) and at night (8) up to elevations of 1000 feet; five Culex species 
were taken at elevations of 200 and 5000 feet. Aedes vexans was taken at night 
at 500 feet to 5000 feet. 

CLASSIFICATION OF THE CULICIDAE 

KEYS TO THE SUBFAMILIES, TRIBES, GENERA, 
AND SUBGENERA 

The Subfamilies 

ADULTS 

Mouth parts not prolonged into a proboscis, extending little beyond the 
clypeus; scales, when present, largely confined to the hind margin of 
the wing Chaoborinae 8 

Mouth parts prolonged into a proboscis, extending far beyond the clypeus; 
scales always present on the wing veins and along the marginal fringe; 
legs with scales; body usually with scales or they may be almost absent 
; . . Culicinae 

LARVAE (4th instar) 

Antennae prehensile, with long and strong apical spines (Fig. 94) 

Chaoborinae 8 

Antennae not prehensile and lacking the strong apical spines Culicinae 

PUPAE 

1. Swimming paddles fused basally, not movable; with apical and lateral 

articulated spines or hairs (Corethrella) Chaoborinae 8 

Swimming paddles free, movable; without long hairs or spines 2 

2. Respiratory horn either almost closed apically or with the spiracular 

opening near the middle; surface of horn with hexagonal reticulations 

Chaoborinae 8 

Respiratory horn open at tip, spiracle at its base Culicinae 

The Tribes of the Culicinae 
ADULTS 
i. Proboscis rigid; basal half stout, the apical half more slender and bent 

8 Not further treated here; adults never take blood. 



MOSQUITOES 313 

sharply backwards; scutellum evenly rounded with marginal hairs 

and scales well distributed Megarhinini 

Proboscis not rigid, of nearly uniform thickness (though the apex may 
be swollen) and the apical half not bent sharply backwards 2 

2. Scutellum evenly rounded, crescent-shaped, or it may be slightly lobed 

(as in Chagasia), without or with few scales but the marginal hairs 
evenly distributed; first tcrgite of abdomen always without scales; 
sternites nearly always bare of scales; palpi of males and females 
as long or nearly as long as proboscis (except in Bironella) (Fig. 125) 

Anophelini 

Scutellum trilobed with the hairs restricted to the lobes; scales nearly al- 
ways present and usually in patches; abdomen with tergites and 
sternites clothed with scales; palpi in the females short; in the males 
long and bushy (Fig. 125) 3 

3. Base of hind coxa in line with the upper margin of the mcron; (Fig. 

99, #); postnotum with a group of bristles (all American species); 
abdomen almost completely free of hairs and usually compressed 

Sabethini 

Base of hind coxa distinctly below upper margin of meron; postnotum 
lacking bristles, smooth (except in some oriental species of Aedes)\ 
abdomen with hairs on hind margins of segments Culicini 

LARVAE ( 4 th instar) 

1. Eighth segment without an elongated siphon or respiratory tube, the 

spiracles sessile Anophelini 

Eighth segment with an elongated siphon or respiratory tube which 
is at least as long as broad 2 

2. Mouth brushes prehensile, each composed of 10 stout rods . . Megarhinini 
Mouth brushes not or rarely prehensile, each composed of 30 or more 

hairs 3 

3. Anal segment with one pair of ventral hairs or tufts instead of a brush; 

siphon usually with numerous hairs or tufts Sabethini 

Anal segment with a ventral brush, usually large but at least four 
separate hairs or tufts; siphon usually with tufts but these in definite 
arrangement Culicini 

PUPAE 
i. Lateral apical hairs of abdominal segments, except the last pair, are 

blunt spines and placed almost exactly at the corners Anophelini 

Lateral apical hairs of abdominal segments placed well before the apical 
corners and each consists of a branching hair or a single hair 2 



3 r 4 MEDICAL ENTOMOLOGY 

2. Outer part of paddle produced beyond the tip of midrib Megarhinim 

Outer part of paddle not longer than midrib 3 

3. Seventh and eighth segments with large posterolateral tufts; paddles 

smooth and lack apical hairs Sabethini 

Abdomen not as described above; paddles with apical hairs Culicini 

Genera and Common Sub genera of Tribe Anophelini 

ADULTS 

1. Scutellum slightly trilobed (South American) Chagasia Cruz 

Scutellum crescent-shaped, evenly rounded 2 

2. Stem of second fork cell wavy Bironella Theobald 

Stem of second fork cell straight Anopheles Meigen 3 

3. Thorax blackish with a broad gray line from neck to scutcllum 

Subgenus Stethomyia Theobald 

Thoracic ornamentation quite otherwise 4 

4. Wings with rarely more than two pale spots on costa; sidepiece of male 

genitalia with i to 3 (usually 2) strong basal spines set on tubercles 

Subgenus Anopheles Meigen 

Wings with 4 or more pale costal spots (Fig. 131) 5 

5. Sidepiece of male genitalia with one spine at base and two beyond. 

(New World species) Subgenus Nyssorhynchits Blanchard 

Sidepiece of male genitalia with several weak spines near base and 

not set on tubercles. (Old World species) 

Subgenus Myzomyia Blanchard 

LARVAE (4th Instar) 

1. Body of larva densely clothed with short hairs in addition to the regu- 

lar hairs; leaflets of palmate tufts greatly expanded apically and each 
ending in a long central hair. Anterior flap of spiracular apparatus 
produced into a long, stout, bristlclike structure Chagasia Cruz 

Body of larva not densely covered with fine hairs; leaflets of palmate 
tufts not as described above; no prolongation of anterior flap of 

. spiracular apparatus 2 

2. Two pairs of palmate hairs on the thorax Bironella Theobald 

At most one pair of palmate hairs on thorax Anopheles Meigen 

Key to Genera of the Tribe Culicini: Adults 
(Modified from Edwards, 1932) 

i. Squama fringed (fringe usually complete); anal vein (6th) reaching 
well beyond the base of cubital fork (fork of 5th vein) 4 



MOSQUITOES 315 

Squama bare (Fig. 131) or with i to 4 short hairs; second marginal cell 
(R 2 ) shorter than its stem; anal vein (6th) ends about opposite of 
cubital fork (fork of 5th vein) 2 

2. Wing membrane lacks microtrichia; second marginal cell (R 2 ) shorter 

than its stem; anal vein (6th) ends about opposite the base of fork 

of 5th vein Uranotaenia Lyn. Arrib. 

Wing membrane with distinct microtrichia 3 

3. Second marginal (R 2 ) cell shorter than its stem; several posterior 

pronotal bristles; wing scales not emarginate at tips. (One species, 

Malaya) Zeugnomyia Leicest. 

Second marginal cell longer than its stem; 2 posterior pronotal bristles; 

wing scales emarginate at tips. (Africa, India, S. Pacific) 

Hodgesia Theobald 

4. Pulvilli present; pleural chaetotaxy well developed but spiracular and 

postspiracular bristles absent 5 

Pulvilli absent or rudimentary; spiracular and postspiracular bristles 
present or absent or one set may be present 6 

5. Antennae much longer than the proboscis; first flagellar segment of 

antenna as long as several of the following segments taken together; 
antennae similar in both sexes, never very bushy. (Sea coasts of the 

Gulf, Caribbean, and West Indies) Dcinoceriies Theobald 

Antennae not much longer than the proboscis; first flagellar segment 
not as long as several of the following segments taken together; male 
antennae very bushy and different from the female. (World-wide in 
distribution) Culcx Linnaeus 

6. Postspiracular bristles absent; claws of female generally simple (except 

in species of Haemagogus) 7 

Postspiracular bristles present (at times only i or 2) ; claws of female 
usually toothed; dorsocentrals and upper sternopleurals nearly always 
well developed 13 

7. Spiracular bristles present (at times only i or 2) 

Culiseta Theobald 

Spiracular bristles absent 8 

8. Pronotal lobes almost touching dorsally; dorsocentral and prescutellar 

bristles absent Haemagogus Williston 

Pronotal lobes well separated; dorsocentral and prescutellar bristles well 
developed 9 

9. Postspiracular area with scales; claws of female usually toothed; palpi 

of female more than half as long as proboscis Armigeres Theobald 



3 i6 MEDICAL ENTOMOLOGY 

Postspiracular area bare; claws of female simple; palpi of female not 
half as long as proboscis 10 

10. All segments of female antennae and last two of male antennae short 

and thick; middle femur with a scale tuft Aedomyia Theobald 

Antennae slender; middle femur without a scale tuft n 

11. First segment of front tarsus longer than the last four taken together; 

4th segment very short, only as long as wide; mesonotum usually 

with narrow longitudinal lines of silvery- white scales 

Orthopodomyia Theobald 

First segment of front tarsus not so long, or as long, as the last four 
taken together; 4th segment not as described above 12 

12. Proboscis of male much swollen apically; of female slightly swollen 

or else cell R 2 (2nd marginal) shorter than its stem 

Ficalbia Theobald 

Proboscis of male or female not swollen apically; cell Ro (2nd marginal) 
as long as its stem (in part) Mansonia Blanchard 

13. Spiracular bristles present, at times only i or 2. (The Americas) 

Vsorophora Rb.-Desvoidy 

Spiracular bristles absent 14 

14. Eyes widely separated; space between and back of the eyes with metal- 

lic silvery scales (African) Eretmapodites Theobald 

Eyes not so widely separated, almost touching; space between and back 
of the eyes not clothed with metallic silvery scales 15 

15. Wing scales mostly narrow (when broad the female claws are toothed) 

16 

Wing scales all very broad; female claws not toothed 

(in part) Mansonia Blanchard 

1 6. Proboscis slender, not recurved at tip in repose; ornamentation varied 

Aedes Meigen 

Proboscis stout, recurved at tip in repose; dark species with flat scales 
on vertex and scute] lum Armigeres Theobald 

LARVAE (4thinstar) 

1. Distal half of air tube (siphon) sharply attenuated and apical portion 

provided with sawlike teeth for penetrating plants 

Mansonia Blanchard 

Air tube (siphon) not as described above 2 

2. Head longer than broad or as long as broad (appearing more or less 

as rounded); 8th abdominal segment with a lateral chitinous plate 



MOSQUITOES 317 

with one row of comblike teeth on its posterior margin; antennae 

not inflated or very large Uranotaenia Lyn. Arrib. 

Head always broader than long; 8th abdominal segment without such 
a plate (except at times in certain Psorophora and all Aedomyia spp. 
but in these the antennae are inflated and flattened) 3 

3. Air tube with pccten; the teeth of the pectcn nearly always denticu- 

late 4 

Air tube without pecten or rarely a few simple teeth and these not 
denticulate 9 

4. Air tube with several pairs of ventral hair tufts (never less than 2 pairs) 

and occasionally scattered dorsal hairs or the air tube is extremely long 

and slender with hair tufts apparently lacking 5 

Air tube not as described above; with never more than a single pair of 
hair tufts or in addition there may be a median ventral line of hair 
tufts 7 

5. Mouth brushes prehensile, often appearing as matted tufts or as rods 

(Subgenus Lutzia) Culex Linnaeus 

Mouth brushes normal, composed of long hairs 6 

6. Head with a prominent pouch on each side enclosing the mandible, 

which has a hairy base Deinocerites Theobald 

Head not as described above; mandibles without a hairy base 

Culex Linnaeus 

7. Air tube with a pair of basal hair tufts only or a pair of basal hairs 

(single) Culiseta Felt 

or 

Air tube with a pair of basal hair tufts and a median row of ventral 
tufts (Subgenus Climactira) Culiseta Felt 

Air tube with a single pair of ventral tufts placed near the middle of 
tube or beyond; if tufts are lacking or vestigial the anal segment is 
completely ringed by the dorsal plate or saddle and pierced by some 
of the tufts of the ventral brush 8 

8. Anal segment completely ringed by the saddle; the saddle is pierced on 

the mid-ventral line by tufts of the ventral brush; air tube often 

swollen and pecten of few teeth Psorophora Rb.-Desvoidy 

Anal segment not completely ringed by the saddle, but, if so, the ventral 
brush is confined posterior to the ring (no tufts pierce the saddle) 

Aedes Meigen 

Haemagogtts Williston 



318 MEDICAL ENTOMOLOGY 

9. Antenna short with a simple hair on shaft; antenna more or less cylin- 
drical, never inflated 10 

Antenna longer with a branched hair on shaft; antenna may be 
cylindrical or inflated or flattened 12 

10. Ventral tuft of air tube large n 

Ventral tuft small and simple. (Only i species, from Malaya) 

Zeugnomyia Leicester 

11. Ventral brush of anal segment well developed with a barred area. 

(Oriental and Australasian) Armigeres Theobald 

Ventral brush of anal segment with never more than four pairs of single 
hairs, usually i or 2 pairs of branched hairs; they never form a barred 
area. (African) Eretmapodites Theobald 

12. Antenna very large, flattened, not cylindrical in cross section. (South 

and Central America, Africa, and Oriental region) 

Aedomyia Theobald 

Antenna never very large and flattened, usually cylindrical in cross 
section 13 

13. Large sclerotized plates present on dorsum of abdominal segments 6 to 

8 or rarely absent Orthopodomyia Theobald 

Sclerotized plates absent on abdominal segments 6 to 8 14 

14. Hair tuft of antenna well removed from apex; anal segment ringed 

by saddle Ficalbia Theobald 

Hair tuft of antenna close to apex; anal segment ringed by saddle . . . 

Hodgesia Theobald 

Hair tuft of antenna before the middle; anal segment not ringed by 

the saddle or dorsal plate Orthopodomyia Theobald 

It is not feasible to offer keys to species of mosquitoes, even the anophelines 
(except those of North America), in a limited textbook. The student is re- 
ferred to the bibliography where he will find references (and references with 
extended bibliographies are double-starred) which will enable him to locate 
keys to the species of nearly any region of the world. In addition to keys he 
must have detailed descriptions and a wealth of illustrations. 

KEY TO THE ANOPHELINES OF NORTH AMERICA 

Adults (Males and Females) 

i. Hind tarsus with apical portion of second and all of third and fourth 
segments white; fifth segment white with a narrow, basal, black 
ring (Subgenus, Nyssorrhynchus) albimanus Wied. 



MOSQUITOES 319 

Tarsal segments of all legs dark or black without white markings 
(Subgenus, Anopheles) 2 

2. Scales of the wings entirely dark or black; apex of wing may have a 

single coppery or light spot 3 

Wings with distinct spots or areas of white or light-colored scales on 
the veins as well as on the costal margin 9 

3. Scales of the wings not grouped in spots but evenly distributed on the 

veins; legs and palpi dark-scaled. A small species that breeds in tree 

holes barberi Coq. 

Scales of the wings grouped in darker spots which are usually very dis- 
tinct; palpi may be dark-scaled or ringed with white 4 

4. Segments of the palpus with narrow white rings at their apices; terminal 

segment with white apex; white or yellowish knee spots (apices of 

femora) present; wing spots usually distinct waU^eri Thco. 

Palpi entirely dark-scaled, rarely any pale scales present 5 

5. Wing spots usually not very distinct; knee spots absent; general 

coloration very dark atropos D. & K. 

Wing spots very distinct; knee spots present; general coloration not so 
dark 6 

6. Apex of wing with a distinct coppery or golden patch of scales; meso- 

notum with a broad, median, longitudinal, whitish (pruinosc) stripe 

7 

Apex of wing without such a spot, uniformly dark 8 

7. Wing 5 to 6 mm. in length; stem vein of second longitudinal vein be- 

yond dark spot with outstanding scales earlei Vargas 

Wing rarely more than 5 mm. in length, frequently less; stem vein of 
second longitudinal vein beyond dark spot with closely appresscd 
scales, none outstanding occidentalis D. & K. 

8. Mesonotum uniformly colored, no distinct stripe; occurs east of the 

Rocky Mountains and is widely distributed from Canada to the 

Gulf of Mexico quadrimaculatus Say 

Mesonotum with a pale pruinose stripe, fading out anteriorly; occurs 
in the Rocky Mountain region and west of it; the dark spots of the 
wings are usually more dense jreeborni Aitken 

9. Costal margin dark except a white or yellowish-white spot at extreme 

apex of wing; vein 6 with three dark spots separated by white scales. 

Stem of 5th vein dark-scaled crucians Wied. 

georgianus King 

Stem of 5th vein all white-scaled bradleyi King 



320 MEDICAL ENTOMOLOGY 

Costal margin of wing with 2 white spots, one near apex and a large one 
at outer third near apex of subcostal vein; vein 6 with only i or 2 dark 
spots 10 

10. Veins 3 and 5 dark-scaled; vein 6 with short basal black spot separated 

by a light area from the dark apical half; wing fringe without pale 

spots at tips of veins; palpus black piinctipennis Say 

Veins 3 and 5 with central areas largely pale-scaled; vein 6 with basal 
half white, apical half black; wing fringe with pale spots at tips of 
veins n 

11. Terminal segment of palpus entirely white; vein 4 pale before fork . . 

pseudopunctipennis Theo. 

Terminal segment of palpus white at base, apical half black; vein 4 
black before the fork jranciscanus McC. 

Males (Based on the Genitalia) 

1. Sidepiece with 4 stout spines i basal, 2 accessory, and i internal (Sub- 

genus Nyssorhynchus) albimanus Wicd. 

Sidepiece with 3 stout spines 2 basal, i internal. (Subgcnus Anopheles) 

2 

2. Mesosome without leaflets 3 

Mesosome with leaflets 4 

3. Dorsal lobe of claspette nearly cylindrical in shape with 3 apical, closely 

appressed, overlapping spines, the outer 2 sharply curved at tips and 
forming a kind of hood; these spines nearly twice as long as the 

lobe barberi Coq. 

Dorsal lobe of claspette as above but with 3 apical, bladelike spines, all 

about the same length and size; spines not as long as the lobe 

jranciscanus McC. 

4. Leaflets of mesosome deeply serrate, varying from 2 to 4 pairs and dif- 

ficult to see pseudopunctipennis Theo. 

Leaflets of mesosome not serrate 5 

5. Sidepiece with numerous scales; dorsal and ventral lobes of each clasp- 

ette fused to form a conical lobe; this lobe bears 5 spines, rarely less; 

lobes of ninth tergite very long and pointed crucians Wied. 

bradleyi King 

georgianus King 

Sidepiece without scales or, rarely, a few present; dorsal and ventral 
lobes of claspette distinct; lobes of ninth tergite usually not so long 
or so pointed 6 



MOSQUITOES 321 

6. Dorsal lobe of claspette with bluntly rounded apical spines, sometimes 

expanded at apices or partially fused 7 

Dorsal lobes of claspette with pointed spines 9 

7. Lobes of ninth tergite short, stout, usually expanded at apices; spines 

of dorsal lobe of claspette not expanded at apices but generally more 

'or less fused and rounded quadrimaculatus Say 

Lobes of ninth tergite long and pointed or slightly rounded; spines of 
dorsal lobe of claspette not as described above 8 

8. Dorsal lobe of claspette with 2 spines fused at their bases and each ter- 

minating in an enlarged and rounded knob; ventral lobe with only 2 
rather large, pointed spines; apical leaflet of mcsosome not twice as 

long as the second leaflet waU{cri Theo. 

Dorsal lobe of claspette with 2 spines, each terminating in a rounded 
knob but each spine arises from a separate tubercle and they arc not 
fused at their bases; apical leaflet of mesosome twice as long as the 
second leaflet atropos D. & K. 

9. Dorsal lobe of claspette with 2 sharply pointed, apical spines, the spines 

so closely associated as to appear as only one; ventral lobe of claspette 
with a large, pointed apical spine, a smaller internal spine, and a 
minute spine between them; lobes of ninth tergite short, stout, and 
slightly expanded apically punctipcnnis Say 

Lobes of claspette not as described above; lobes of the ninth tergite long 

or short, but if short, pointed apically or expanded 10 

10. Dorsal lobe of claspette with 2 or 3 sharply pointed spines, the spines 
so closely associated as to appear almost as one; lobes of the ninth 
tergite long, narrow, and rounded apically jreeborni Aitken 

Dorsal lobe of claspette similar to that described above; lobes of ninth 
tergite short, broad, and expanded at apex earlei Vargas 

Dorsal lobe of claspette similar to that described above; lobes of ninth 

tergite somewhat longer, narrow, and rarely expanded at apex 

occidcntalis D. & K. 

Larvae (Fourth Ins far) 

1. Abdomen with plumose, lateral hairs on the first six segments; all head 

hairs small, single. Larvae occur in tree holes barberi Coq. 

Abdomen with plumose, lateral hairs on the first three segments only; 
frontal hairs (Nos. 5, 6, and 7) large and plumose 2 

2. Palmate hairs well developed on abdominal segments i to 7; both inner 



322 MEDICAL ENTOMOLOGY 

and outer clypeal hairs long and slender; inner clypeal hairs widely 
separated and feathered on outer half; outer clypeal hairs with minute 

branches on the outer half albimanus Wied. 

Palmate hairs well developed on abdominal segments 2 or 3 to 7; inner 
and outer clypeal hairs not as described above 3 

3. Outer clypeal hairs not densely branched dichotomously 4 

Outer clypeal hairs densely branched dichotomously 6 

4. Inner, outer, and posterior clypeal hairs long, single, subcqual, and 

widely separated at their bases 5 

Inner and outer clypeal hairs long, usually with i to 5 branches near the 
tips; posterior clypeal hairs short and may be branched; inner clypeal 
hairs are closely approximated at their bases atropos D. & K. 

5. Inner angle of each posterior plate of respiratory apparatus produced into 

a long, sclerotized tail. (In living larvae these tails are bent upward 

at right angles to the plate and project through the water) 

psettdopunctipennis Theo. 

Inner angle of each posterior plate rounded and not produced into a 
tail ' franciscanus McC. 

6. Abdominal segments 4 and 5 with 2 conspicuous hair tufts (Nos. 2 and 

o) anterior to the palmate tuft; these tufts are approximately equal 

in size and have 4 to 9 branches crucians Wied. 

Abdominal segments 4 and 5 with only i hair tuft (No. 2) anterior to 
each palmate tuft; hair o vestigial or lacking, or, if present, the inner 
clypeal hairs are sparsely feathered toward the tips 7 

7. Inner clypeal hairs divided into 2 or 3 branches or feathered toward the 

tips 8 

Inner clypeal hairs unbranched (rarely divided into 2 branches near the 
middle) 9 

8. Inner clypeal hairs closely approximate, so close that an extra tubercle 

of the same size cannot be placed between their bases; each clypeal hair 
is sparsely feathered on the apical half; occipital hairs (Nos. 8 and 9) 

small, each with 2 to 4 branches wallferi Theo. 

Inner clypeal hairs not so closely placed that an extra tubercle of the 
same size cannot be inserted between their bases; inner clypeal hairs 
with 2 or 3 branches near the middle; occipital hairs with many 
branches and stout shafts earlei Vargas 

9. Inner clypeal hairs separated at their bases by at least the diameter of one 

tubercle; palmate tufts well developed on segments 3 to 7; palmate 
tuft on segment 2 frequently well developed; occipital hairs well 



MOSQUITOES 323 

developed with 8 to 10 branches quadrimaculatus Say 

occidentdis D. & K. 

Inner clypeal hairs so closely placed that an extra tubercle cannot be 

inserted between their bases 10 

10. Palmate tufts present only on segments 4 to 6 gcorgianus King 

Palmate tufts present on segments 3 to 7 n 

u. Palmate tufts on segments 3 and 7 smaller than the others; inner 

clypeal hairs normally placed close together bradleyi King 

Palmate tufts on segments 3 and 7 of the same size as the others 12 

12. Hair No. 2 on abdominal segments 4 and 5 multiple (4- to 5-branched) 

jrceborni Aitken 

Hair No. 2 on segments 4 and 5 single punctipennis Say 

REFERENCES 
General Worlds 

**American Association for the Advancement of Science. A symposium on hu- 
man malaria. (Pub. 15.) Washington, D.C., 1941. 

Rlanchard, R. Les moustiques. Paris, 1905. 

*Boyd, M. F. An introduction to malariology. Cambridge, Mass., 1930. 

**Covell, G. The present state of our knowledge regarding the transmission of 
malaria by the different species of anopheline mosquitoes. Rec. Mai. Surv. Ind., 
2, 1931. 

*Edwards, F. W. Diptera, fain. Culicidae. In P. Wytsman, Cenera Insectorum, 
fasc. 194, Bruxelles, 1932. 

Giles, G. M. A handbook of the gnats or mosquitoes, giving the anatomy and 
life history of the Culicidae. 2nd ed. London, 1902. 

Click, P. A. The distribution of insects, spiders and mites in the air. U.S. Dept. 
Agr., Tech. Bull. 673, 1939. 

Kumm, H. W. The distribution of malaria carrying mosquitoes. Amer. Jl. Hyg., 
Monograph Ser. No. 10, 1929. 

. The distribution of yellow fever vectors. Ibid., No. 12, 1931. 

**MacGregor, M. E. Mosquito surveys; a handbook for anti-malaria and anti- 
mosquito workers. London, 1937. 

**Marshall, J. H. The British mosquitoes. London, 1938. 

Martini, E. Ueber Stechmikken. Arch. Schiff. Trop. Hyg., Beihft., 24: 1-167, 
1920. 



Publications on the morphology, bionomics, and classification of mosquitoes number 
many thousands. The following references will include, as far as possible, a fair distribu- 
tion from all parts of the world so that any student will find some article that will aid 
him in his work. Many of die articles or books also cover the field of malariology. 



324 MEDICAL ENTOMOLOGY 

**Matheson, R. The mosquitoes of North America. Ithaca, N.Y., 1944. 
*Russell, P. F., Rozeboom, L. E., and Stone, A. Keys to anopheline mosquitoes 

of the world. Amer. Ent. Soc. Philadelphia, 1943. (Includes adults and 

larvae.) 
Theobald, F. V. A monograph of the Culicidae or mosquitoes. London (British 

Museum), 1901-1910. 5 vols. 

Main ly Morph ological 

Baisas, F. E. Notes on Philippine mosquitoes. IV, VI. Philip. Jl. Sci., 59: 65-84, 
1936; 61: 205-220, 1936. 

. Notes on Philippine mosquitoes. VII. Philip. Bur. Hlth. Mon. Bull., 18: 

175-232, 1938. (The three papers by Baisas deal largely with pupal chaetotaxy.) 

Barraud, P. J., and Covell, G. The morphology of the buccal cavity in anopheline 
and culicine mosquitoes. Ind. Jl. Med. Res., 15: 671-680, 1928. 

Christophers, S. R. The development and structure of the terminal segments 
and hypopygium of the mosquito, with observations on the homologies of the 
terminal segments of the larva. Ibid., 10: 530-572, 1922. 

. The structure and development of the female genital organs and hy- 
popygium of the mosquito. Ibid., pp. 698-720, 1923. 
-, and Barraud, P. J. Descriptive terminology of male genitalic characters of 



mosquitoes. Ibid., pp. 827-835, 1923. 
Edwards, F. W. The nomenclature of the parts of the male hypopygium of 

Diptera, Nematocera, with special reference to mosquitoes. Ann. Trop. Med. 

Hyg., 14: 23-40, 1920. 
*Freeborn, S. B. The terminal abdominal structures of male mosquitoes. Amer. 

Jl. Hyg., 4: 188-212, 1924. 
*Hurlbut, H. S. A study of the larval chaetotaxy of Anopheles wal^cn Theobald. 

Ibid., 28: 149-173, 1938. 
Macfie, J. W. S. The chaetotaxy of the pupa of Stegomyia jasciata. Bull. Ent. 

Res., 10: 161-169, T 920. 
Martini, E. Ueber einige fur das System bedeutungsvollc Merkmale der Stech- 

miicken. Xool. Jahrb., Abt. Syst., 46: 517-590, 1923. 
Nuttall, G. H. F., and Shipley, A. The structure and biology of Anopheles. Jl. 

Hyg., i: 45-77, 269-276, 451-482, 1901. 
Senevet, G. Contribution a 1'etude des nymphes des Culicides. Arch. Inst. 

Pasteur Algerie, 8: 297-382, 1930. 
. Contribution a 1'etude des nymphes d'anophelines. Ibid., 9: 17-112, 1931; 

10 : 204-254, 1932; 12: 29-76, 1934. 

Mainly Biological 

**Aitken, T. H. G. Studies of the anopheline complex of western America. 

Univ. Calif. Pub. Ent., 7: 273-364, 1945. 
Atkin, E. E., and Bacot, A. Stegomyia jasciata. Parasitology, 2: 482-536, 1917. 



MOSQUITOES 325 

Baker, F. C. The effect of photoperiodism on resting, treehole mosquito larvae. 

Can. Ent., 67: 149-153, 1935. 
Balfour, M. C. Studies on the bionomics of North American anophelines. Winter 

activities of anophelines in coastal North Carolina (36 N. Lat.). Amer. Jl. 

Hyg., 8: 68-76, 1928. 
Bang, F. B., Quinby, G. E., and Simpson, T. W. Anopheles walferi (Theo.); 

a wild-caught specimen harboring malaria plasmodia. U.S. Pub. Hlth. Repts., 

55: 119-120, 1940. 
Barber, M. A. The food of anopheline larvae food organisms in pure culture. 

Ibid., 42: 1494-1510, 1927. 
. The food of culicine larvae food organisms in pure culture. Ibid., 43: 

11-17, I 9 2 $- 
, and Komp, W. H. W. Breeding places of Anopheles larvae in the Yazoo- 

Mississippi delta. Ibid., 44: 2457-2462, 1929. 
, Komp, W. H. W., and Hayne, T. B. Malaria in the prairie rice regions 

of Louisiana and Arkansas. Ibid., 41: 2527-2549, 1926. 
, Komp, W. H. W., and Hayne, T. B. Some observations on the winter 

activities of Anopheles in southern United States. Ibid., 39: 231-246, 1924. 
Bates, M. The natural history of mosquitoes. New York, 1949. 
. Observations on the distribution of diurnal mosquitoes in a tropical forest. 

Ecology, 25: 159-170, 1944. 
. Oviposition experiments with anopheline mosquitoes. Amcr. Jl. Trop. 

Med., 20: 569-583, 1940. 
Beattie, M. V. F. Physico-chemical factors in relation to mosquito breeding in 

ponds. Jl. Ecol., 18: 67-80, 1930. 
, and Howland, L. J. The bionomics of some tree-hole mosquitoes. Bull. 

Ent. Res., 20: 45-58, 1929. 
Boyd, M. F. Studies on the bionomics of North American anophelines. I. The 

number of annual generations of A. quadrimaculatus . II. Physical and chemi- 
cal factors in their relations to the distribution of larvae in northeastern North 

Carolina. III. Some observations on imagines. Amer. Jl. Hyg., 7: 264-275, 

1927; 9: 346-370, 1929; 12: 449-466, 1930. 
, and Foot, Helen. Studies on the bionomics of North American anophelines. 

The alimentation of anopheline larvae and its relation to their distribution in 

nature. Jl. Prev. Med., 2: 219-242, 1928. 
, and Weatherbee, A. A. Studies on the bionomics of North American 

anophelines. V. Winter activities of Anopheles imagines in coastal North 

Carolina (36 N. Lat.). Amer. Jl. Hyg., 9: 682-694, 1929. 
Bradley, G. H. The natural breeding places of Anopheles mosquitoes in the 

vicinity of Mound, Louisiana. Amer. Jl. Trop. Med., 4: 199-223, 1924. 
. Some factors associated with the breeding of Anopheles mosquitoes. Jl. 

Agr. Res., 44: 381-399, 1932. 



326 MEDICAL ENTOMOLOGY 

Bull, C. G., and Reynolds, B. D. Preferential feeding experiments with anopheline 
mosquitoes. II. Amer. Jl. Hyg., 4: 109-118, 1924. 

, and Root, F. M. Preferential feeding experiments with anopheline mos- 
quitoes. I. Ibid., 3: 514-520, 1923. 

Buxton, P. A. Further studies upon the chemical factors affecting the breeding 
of Anopheles in Trinidad. Bull. Ent. Res., 25: 491-494, 1934. 

Davis, N. C., and Shannon, R. C. The blood feeding habits of Anopheles pseu- 
dopunctipennis in northern Argentina. Amer. Jl. Trop. Med., 8: 443-448, 
1928. 

Dozier, H. L. Observations on breeding places and winter activities of mos- 
quitoes in the vicinity of New Orleans, Louisiana. Proc. Ent. Soc. Wash., 
38: 148-155, 1936. 

Dunn, L. H. Observations on the oviposition of Aedes aegypti Linn, in relation 
to distance from habitation. Bull. Ent. Res., 18: 145-148, 1927. 

**Eyles, D. E. A critical review of the literature relating to the flight and dis- 
persion habits of anopheline mosquitoes. U.S. Pub. Hlth. Bull. 287, 1944. 

, and Bishop, L. R. An experiment on the range of dispersion of Anopheles 

quadrimaculatus. Amer. Jl. Hyg., 37: 239-245, 1943. 

Feng, L. C. The hibernation mechanism of mosquitoes. Arch. SchirT. Trop. 
Hyg., 41 1331-337, 1937. 

Freeborn, S. B. The seasonal life history of Anopheles maculipcnnis with reference 
to humidity requirements and "hibernation." Amer. Jl. Hyg,, 16: 215-223, 
1932. 

Frohne, W. C. Anopheline breeding: suggested classification of ponds based on 
characteristic desmids. U.S. Pub. Hlth. Repts., 54: 1363-1387, 1939. 

Frost, F. M., Herms, W. B., and Hoskins, W. M. The nutritional requirements of 
the larva of the mosquito, Theobaldia incident Thorn. Jl. Exp. Zool., 73: 461- 
479, 1936. 

Griffitts, T. H. D. Winter hibernation of Anopheles larvae. U.S. Pub. Hlth. 
Repts., 33: 1996-1998, 1918. 

Haddow, A. J. The mosquitoes of Bwamba County, Uganda. II. Biting activity 
with special reference to influence of microclimate. Bull. Ent. Res., 36: 33-73, 
1945. III. The vertical distribution of mosquitoes in a banana plantation and 
the biting cycle of Aedes simpsoni Theo. Ibid., pp. 297-304, 1945. 

, et al. The mosquitoes of Bwamba County, Uganda. V. The vertical distri- 
bution and biting cycle of mosquitoes in rain forest with further observations on 
microclimate. Ibid., 37: 301-330, 1947. 

Hearle, E. The life history of Aedes flavescens Miiller. Trans. Roy. Soc. Canada, 
23: 85-102, 1929. 

Herms, W. B., and Frost, F. M. A comparative study of the eggs of California 
anophelines. Jl. Parasit., 18: 240-244, 1932. 

Hinman, E. H. Biological notes on Uranotaenia spp. in Louisiana. Ann. Ent. 
Soc. Amer., 28: 404-407, 1935. 



MOSQUITOES 327 

. Predators of the Culicidae (mosquitoes). I. The predators of larvae and 

pupae, exclusive of fish. II. Predators of adult mosquitoes. Jl. Trop. Med. 
and Hyg., 37: 129-134, 145-150, 1934. 

. A study of the food of mosquito larvae (Culicidae). Amer. Jl. Hyg., 12: 

238-270, 1930. 

. The winter breeding and activity of culicine mosquitoes at New Orleans 

30 N. Lat.). Amer. Jl. Trop. Med., n: 459-467, 1931. 

, and Hurlbut, H. S. A study of winter activities and hibernation of Anoph- 
eles quadrimaculatus in the Tennessee Valley. Ibid., 20: 431-446, 1940. 

Hurlbut, H. S. Further notes on the overwintering of the eggs of Anopheles 
wal\en with a description of the eggs. Jl. Parasit., 24: 521-526, 1938. 

Jobling, B. The efTect of light and darkness on oviposition in mosquitoes. Trans. 
Roy. Soc. Trop. Med. Hyg., 29: 157-166, 1935. 

King, W. V. Notes on Culex erraticus and related species in the United States. 
Ann. Ent. Soc. Amer., 30: 345-357, 1937. 

, and Bull, G. The blood feeding habits of malaria-carrying mosquitoes. 

Amer. Jl. Hyg., 3: 497~5 I 3> T 9 2 3- 

MacCreary, D. Comparative density of mosquitoes at ground level and at an 
elevation of approximately one hundred feet. Jl. Kcon. Ent., 34: 174179, 1941. 

, and Stearns, L. A. Mosquito migration across Delaware Bay. N. J. Mosq. 

Exterm. Assoc. Proc., 24: 188-197, 1937. 

McNeel, T. E. Observations on the biology of Mansonia perttirbans (Walk.). 
Ibid., 19: 91-96, 1932. 

Matheson, R. The efTect of Char a fragilis on mosquito development, with a note 
on a new larviciclc. Ibid., 15: 77-86, 1928. 

. The utilization of aquatic plants as aids in mosquito control. Amer. 

Natur., 641,56-86, 1930. 

, Brunett, E. L., and Brody, A. L. The transmission of fowl pox by mos- 
quitoes. Poultry Sci., 10: 211-223, 1931. 

, and Hinman, E. H. Chara frugilis and mosquito development. Amer. Jl. 

Hyg., 8: 279-296, 1928. 

, and Hurlbut, H. S. Notes on Anopheles wal^erl Theobald. Amer. Jl. 

Trop. Med., 17: 237-242, 1937. 

New Jersey Mosquito Extermination Association. Proceedings . . . , Vol. I-. 
New Brunswick, N.J., 1914-. Annual volumes contain a wealth of informa- 
tion. 

Perez, M. An anopheline survey of the state of Mississippi. Amer. Jl. Hyg., u: 
696-710, 1930. 

Pinto, C. Disseminac.ao da malaria pela avic.ao; biologia do Anopheles gambiae 
e autrous anofelineos do Brasil. Mem. do Instit. Oswaldo Cruz, 34: 293-430, 
1939. 

Rozeboom, L. E. The relation of bacteria and bacterial filtrates to the develop- 
ment of mosquito larvae. Amer. Jl. Hyg., 21: 167-179, 1935. 



328 MEDICAL ENTOMOLOGY 

Rudolfs, W. The composition of water and mosquito breeding. Ibid., 9: 160- 

180, 1929. 
Shannon, R. C. The environment and behaviour of some Brazilian mosquitoes. 

Proc. Ent. Soc. Wash., 33: 1-27, 1931. 
Smith, G. E., Watson, R. B., and Crowell, R. C. Observations on the flight range 

of Anopheles quadrimaculatus Say. Atner. Jl. Hyg., 34: 102-113, 1941. 
Smith, J. B. Report of the New Jersey Agricultural Experiment Station upon 

the mosquitoes occurring within the state, their habits, life history, etc. Trenton, 

N.J., 1904. 

Soper, F. L., and Wilson, D. B. Anopheles gambiae in Brazil. New York, 1943. 
Stage, H. H. Some examples of mosquito ecology in the Pacific Northwest. N. J. 

Mosq. Exterm. Assoc. Proc., 29: 123-124, 1942. 
, and Yakes, W. W. Some observations on the amount of blood engorged 

by mosquitoes. Jl. Parasit., 22: 298-300, 1936. 
Trager, W. The chemical growth factors required by mosquito larvae. Biol. 

Bull., 75: 75-84, 1938. 
. On the nutritional requirements of mosquito larvae (Aedes aegypti). 

Amer. Jl. Hyg., 22: 475-493, 1935. 
. The utilization of solutes by mosquito larvae. Biol. Bull., 71: 343-352, 

1936. 

Mainly Taxonomic 

NEARCTIC REGION 

Bradley, G. H. On the identification of mosquito larvae of the genus Anopheles 
in the United States. South. Med. JL, 29: 859-861, 1936. 

**Carpenter, S. J., Middlekaufl, W. W., and Chamberlain, R. W. The mosquitoes 
of the southern United States east of Oklahoma and Texas. Amer. Mid. Nat., 
Monograph 3, 1946. 

*Dyar, H. G. The mosquitoes of the Americas. Carnegie Inst. Wash., Pub. 
No. 387, 1928. 

**Howard, L. O., Dyar, H. G., and Knab, F. The mosquitoes of North and 
Central America and the West Indies. Ibid., No. 159, 1912-1917. 4 vols. 

*King, W. V., and Bradley, G. H. General morphology of Anopheles and classi- 
fication of the Ncarctic species. Amer. Assoc. Adv. Sci., Pub. No. 15: 63-70, 
1941. 

** , Bradley, G. H., and McNeel, T. E. The mosquitoes of the southeastern 

United States. U.S. Dept. Agr., Misc. Pub. 336, 1942. 

**Matheson, R. The mosquitoes of North America. 2nd ed. Ithaca, N.Y., 
1944. 

Root, F. M. The larvae of American Anopheles mosquitoes in relation to classifica- 
tion and identification. Amer. Jl. Hyg., 2: 379-393, 1922. 



MOSQUITOES 329 

Ross, E. S., and Roberts, H. R. Mosquito atlas. Part I. The Nearctic Anopheles. 

Part II. Old World Anophelines. Amer. Ent. Soc., Philadelphia, 1943. 
**Simmons, J. S., and Aitken, T. H. G. The anopheline mosquitoes of the 

northern half of the Western hemisphere and of the Philippine Islands. U.S. 

Army, Med. Bull. 59, 1942. 

Many of the states of the United States have issued special bulletins either by 
their State Agricultural Colleges or their health departments on the mosquitoes 
of their respective areas. 

NEOTROPICAL REGION 

Arribalzaga, Lynch F. Diptcrologia argentina. Rev. Mus. de La Plata, i: 457- 

477, 189052: 134-170, 1891. 

Bonne, C., and Bonne- Wcpster, J. Mosquitoes of Surinam. Amsterdam, 1925. 
Deane, L. M., Causey, O. R., and Deane, M. P. Studies on Brazilian anophelines 

from the northeast and Amazon regions. Amer. Jl. Hyg., Monograph 18, 1946. 
, Causey, O. R., and Deane, M. P. Notas sobre a distribute, no e a biologia dos 

anofelinos das regidnes nordestina e amazunica do Brasil. Rev. Serv. cap. Saude 

Pub. Ano. i (4): 827-965, 1948. 
Dyar, H. G. The mosquitoes of the Americas. Carnegie Inst. Wash., Pub. No. 

387, 1928. 

. The mosquitoes of Panama. Ins. Ins. Mens., 13: 101-195, T 93- 

Galvas, A. G. Biologia y distribution geograhca de los Anophelinos en Colombia. 

Rev. Facult. Medicina, 12, 1943. 
Howard, L. O., Dyar, H. G., and Knab, F. The mosquitoes of North and Central 

America and the West Indies. Carnegie Inst. Wash., Pub. No. 159, 1912- 

1917. 
Komp, W. H. W. The anopheline mosquitoes of the Caribbean region. Nat. 

Inst. Hlth., Bull. No. 179, 1942. 

. The classification and identification of the Anopheles mosquitoes of Mex- 
ico, Central America and the West Indies. Amer. Assoc. Adv. Sci., Pub. No. 

15: 88-97, i94i- 
. The species of the subgenus Kertcszia of Anopheles. Ann. Ent. Soc. Amer., 

30: 49 2 ~5 2 4 !937- 
Kumm, H. W., Komp, W. H. W., and Ruiz, H. The mosquitoes of Costa Rica. 

Arner. Jour. Trop. Med., 20: 385-422, 1940. 

, and Zuniga, H. The mosquitoes of El Salvador. Ibid., 22: 399-415, 1942. 

Lane, J. Catalogo dos mosquitos neotropicos. S. Paulo, Brasil, [ 1939]. 

, and Cerqueira, N. L. Os Sabetinos da America (Diptera, Culicidae). 

Arquivos Zool. Estad. Sao Paulo, 7: 473-849, 1942. 
Martini, E. Los mosquitos de Mexico. Depart, de Salub. Pub. Mexico, Bol., 

Tec. Ser. A, No. i, 1935. 

Peryassu, A. G. Os Anophelinos do Brasil. Arch. Mus. Nac., 23: 1-99, 1921. 
. Os Culicideos do Brasil. Rio de Janeiro, 1908. 



330 MEDICAL ENTOMOLOGY 

Root, F. M. Studies on Brazilian mosquitoes. I-IV. Amer. Jl. Hyg., 6: 684- 

717, 1926; 7: 470-480, 574-598, 599-605, 1927. 
Senevet, G. Les moustiques de la Guyane franchise (Misson 1934). Arch. Inst. 

Pasteur Algerie, 15: 352-382, 1937. 
, and Abonnenc, E. Les moustiques de la Guyane franchise. Le genre Culex. 

Ibid., 17: 62-134, 1939. 
, and Abonnenc, E. Quelques anophelines de la Guyane franchise. Ibid., 

16: 486-512, 1938. 

PALEARCTIC REGION 

Edwards, F. W. A revision of the mosquitoes of the palearctic region. Bull. Ent. 

Res., 12: 262-351, 1921. 
. Una revisione delle zanzare delle regioni paleartiche. Riv. Malariologia, 

5 : 393~466j 613-653, 1926. 
Hackett, L. W., and Missiroli, A. The varieties of Anopheles maculipcnnis and 

their relation to the distribution of malaria in Europe. Ibid., 14: 45-109, 1935. 
*Kirkpatrick, T. W. The mosquitoes of Egypt. Cairo, 1925. 
Martini, E. Beitrage zur medizinischen Entomologie und zur Malaria- 

Epidemiologie des unteren Wolgagebiets. Abh. Gebiete Auslandsk., Hamburg 

Univ., 29, Ser. D, 1928. 

. Culicidae. In E. Lindner, Die Fliegen de palaearktischen Region. Stutt- 
gart, 1929-1931. 
*Seguy, E. Histoire naturelle des moustiques de France. Paris, 1923. 

. Les moustiques d'Afrique Mineure, de I'Egypte et de la Syrie. Paris, 1924. 

Stackelberg, A. A. Faune de 1'URSS, insectes, dipteres, fam. Culicidae (subfam. 

Culicinae). Inst. Zool. Acad. Sci. URSS (Moscow) 3, No. 4 (Nouv. Ser. No. 

JI )> 1937- 

ETHIOPIAN REGION 

Bedford, G. A. H. South African mosquitoes. S. Afr. Dept. Agr., i3th and 

i4th Rept. Vet. Res., pp. 883-990, 1928. 
Bequaert, J. Medical entomology [Diptera]. In R. P. Strong, et al., The African 

republic of Liberia and the Belgian Congo, pp. 825-846. Cambridge, Mass., 

'93 1 - 
*Edwards, F. W. Culicine adults and pupae. (Mosquitoes of the Ethiopian 

region, Vol. III.) London, 1941. 
*Evans, A. M. Anophelini, adults and early stages. (Mosquitoes of the Ethiopian 

region, Vol. II.) London, 1938. 
*Hopkins, G. H. E. Larval bionomics of mosquitoes and taxonomy of culicine 

larvae. (Mosquitoes of the Ethiopian region, Vol. I.) London, 1936. 
**Meillon, B. de. The Anophelini of the Ethiopian geographical region. S. Afr. 

Inst. Med. Res., Vol. 10 (No. 49), 1947. 



MOSQUITOES 331 

ORIENTAL REGION 

*Barraud, P. J. Family Culicidae: tribes Megarhinini and Culicini. (The fauna 
of British India: Diptera, Vol. V.) London, 1934. 

. A revision of the culicine mosquitoes of India. Parts 1-26. Ind. }1. Med. 

Res., 10-17, 1923-1929. 

*Christophers, R. S. Family Culicidae: tribe Anophelini. (The fauna of Brit- 
ish India: Diptera, Vol. IV.) London, 1933. 

Gater, B. A. R. Aids to the identification of anopheline larvae in Malaya. Singa- 
pore, 1934. 

. Aids to the identification of anopheline imagines in Malaya. Singapore, 

'935- 
Li, Feng-Swen, and Wu, Shih-Cheng. The classification of mature larvae of 

Chinese anopheline mosquitoes. Entom. and Phytopath. (Hangchow), 2: 

3-14, 22-32, 43-52, 62-66, 82-93, 1934. 
, and Wu, Shih-Cheng. On the known species of Chinese Culicini with a 

few species of other tribes. Ibid., 3: 44-98, 1935. 
Marishita, K. Classification of the Formosan anophelines with a key to species. 

Trans. Nat. Hist. Soc., Formosa, 26: 347-355, 1936. 
*Puri, I. M. Larvae of anopheline mosquitoes with full descriptions of those of 

the Indian species. Ind. Med. Res. Mem. No. 21: 1-227, 1931. 
Swellengrebel, N. H., and Rodenwaldt, E. Die Anophelen von Nicderlandisch- 

Ostindien. 3rd eel. lena, 1932. 
Toumanoff, C. L'anophelisme en Extreme-Orient. Paris, 1936. 

AUSTRALIAN REGION 

Edwards, F. W. A synopsis of the adult mosquitoes of the Australian region. 

Bull. Ent. Res., 14: 351-399, 1924. 
Knight, K. L., Bohart, R. M., and Bohart, G. E. Keys to the mosquitoes of the 

Australasian region. Nat. Res. Council, Washington, D.C., 1944. Mimeo- 
graphed. 
Lee, D. J. An atlas of the mosquito larvae of the Australasian region. Tribes 

Megarhinini and Culicini. Melbourne, 1944. 
, and Woodhill, A. R. The anopheline mosquitoes of the Australasian region. 

Dept. Zool., Univ. Sydney, Monograph 2, 1944. 
Mackerras, I. W. Notes on Australian mosquitoes. Proc. Linn. Soc. N. South 

Wales, 52: 33-41, 284-298, 1927; 62: 259-262, 1937. 
Taylor, F. H. The Anopheles of the Australian region. Trans. Cong. Far East. 

Assoc. Trop. Med. (7th Cong.), 3: 143-164, 1930. 
. A check list of the Culicidae of the Australian region, Univ. Sydney, Sch. 

Pub. Hlth. Trop. Med., No. i, 1934. 



332 MFDICAL ENTOMOLOGY 

AREAS IN AND ABOUT THE WESTERN PACIFIC OCEAN 

Bohart, R. M. A synopsis of the Philippine mosquitoes. U.S. Navy Res., 

NAVMED No. 580, 1945. 

* . A key to the Chinese culicine mosquitoes. Ibid., No. 961, 1946. 

* , and Ingram, R. L. Mosquitoes of Okinawa and the islands of the central 

Pacific. Ibid., No. 1055, 1946. 
*Tsai-Yu, H., and Bohart, R. M. The mosquitoes of Japan and their medical 

importance. Ibid., 1095, 1946. 
U.S. Navy, Bureau of Medicine and Surgery. The distribution of mosquitoes of 

medical importance in the Pacific area. NAVMED 983, 1946. 



CHAPTER XI 



Mosquitoes in Relation to 
Human Welfare 



MOSQUITOES have always plagued man and animals. They have 
limited and still limit man's occupation of many regions of the globe. 
Always considered as abominable pests about which he knew little and 
cared less, he was suddenly awakened to their extreme importance by the 
discovery by Ronald Ross, in 1898, that they are the transmitters of malaria 
or ague. Long before this, in 1878-1879, Patrick Manson had shown that) 
mosquitoes were the intermediate hosts of Wuchcrcria (Filaria) bancrojti, 
a roundworm that causes serious diseases of man. This discovery had not at- 
tracted much notice as the diseases caused by this worm were not known 
and even yet are not well understood. The incrimination of Aedes aegypti 
(the tiger mosquito) as a vector of yellow fever by Dr. Carlos Finlay (1881- 
1900) and the final proof in 1900 by Reed, Carroll, Lazear, and Agramonte 
aroused the greatest interest in the mosquito problem. At present, mos- 
quitoes are regarded as probably the most important group of all our blood- 
sucking insects. In general, mosquitoes may be said to aflect human welfare 
in the following ways: 

1. Direct irritation caused by their bites. 

2. Diseases of man which are transmitted through the agency of mosquitoes. 

3. Diseases of domestic and game animals which are transmitted by mos- 
quitoes. 

4. Reduction in land, real estate, and other property values, due to the 
excessive abundance of mosquitoes. 

DIRECT IRRITATION 

To many persons the bites of mosquitoes are only a temporary annoyance; 
some do not notice their bites; but many people suffer greatly even from a 



334 MEDICAL ENTOMOLOGY 

few bites. The number of people who appear almost immune to mosquito 
attacks is probably not large, and this immunity may be confined to the bites 
of mosquitoes present in their region. Other species of mosquitoes may cause 
them great annoyance. As this phase of the mosquito problem has never been 
sufficiently stressed, I desire to call particular attention to it, especially at this 
time when so much emphasis is placed on living out of doors to conserve our 
health(Mosquitoes probably affect young children, particularly babies, more 
than we know. To many people the bites are very severe, causing swellings 
and severe itching, followed by incessant scratching and the formation of 
pustules. This is followed by restlessness, loss of sleep, nervous irritation, and 
a determination to avoid mosquito areas at all costs. In many persons the 
lesions caused by mosquito bites remain for months and retain an itching 
sensation.)Frequently mosquito outbreaks may assume such proportions that 
all outdoor work has to be abandoned, and when this occurs year after year 
the development of the district is greatly retarded if not entirely abandoned. 
Bishopp (1933) reported the deaths of 173 head of livestock in Florida due to 
attacks of Psorophora confmnis, and the milk supply of the area was reduced 
1000 gallons per day. (When mosquitoes are abundant, domestic animals 
sufifer, especially during the evening and night hours. In housed animals such 
attacks may be greatly reduced by the use of DDT {see pp. 389-391). 

DISEASES TRANSMITTED BY MOSQUITOES 

At least thirteen important human diseases of wide distribution are trans- 
mitted by mosquitoes and in most cases only by mosquitoes. If the transmit- 
ting mosquitoes could be eliminated, the diseases would largely disappear. 
These are malaria (four kinds), yellow fever, dengue, filariasis (two), en- 
cephalitis (at least four different diseases), and Rift Valley fever. 

MALARIA 

/Malaria, according to/Boyd (1930), is the worst scourge of mankind. The 
disease is caused by-^minute protozoan that invades the red corpuscles (Figs. 
132,133). There are known to be four distinct species of malarial parasites, 
and each produce a distinct type of disease. The parasites are known as 
Plasmodium vivax (Fig. 132), causative agent of benign tertian or vivax 
malaria; Plasmodium malariae, causative agent of quartan malaria; Plasmo- 
dium falciparum, the agent of malignant,-subtertian, pernicious, or aestivo- 
autumnal malaria; and P. ovale, the causative agent of ovale malaria^ The 
common and most prevalent type of malaria in North America is the tertian. 



MOSQUITOES AND HUMAN WELFARE 335 

Pernicious or aestivo-autumnal malaria occurs in the states bordering on the 
Gulf of Mexico. According to Hoffman (1916), the prevalence of the various 
types of malaria in the southern states is about 65 per cent for tertian, 13 per 
cent for quartan, and 22 per cent for aestivo-autumnaU Malaria is one of the 
most widely distributed of human diseases^ It occurs in most of the great 
fertile regions of the earth; its present distribution and extent of endemicity is 
shown in Fig. 134. 










Pig, 132, Malaria parasites in human blood. Upper row: Plasmodium vivax in various 
stages in the formation of merozoites. Lower row: Plasmodium jalciparum in placental 
blood, showing the formation of merozoites and the marked dot of pigment. Note that 
in P. vivax the red cells are greatly enlarged while in P. jalciparum there is no apparent 
enlargement of the red cells. (Photographs by the author.) . 

In order to understand the essential role played by anopheline mosquitoes 
in the transmission of malaria, a very brief outline of the life cycle of Plasmo- 
dium vivax is here presented. Plasmodium vivax, in man, lives and multiplies 
asexually in the red blood corpuscles (Fig. 132). This is known as the asexual 
cycle (the human or intrinsic phase). As the parasites grow (Fig. 133 1-3) 
they cause the red cells to become enlarged (not true of Plasmodium falci- 
parum) and absorb the cell contents. At the end of about 40 hours, the 
trophozoite is mature and is now called a schizont (5). During the next eight 




Fig. 733. Diagrammatic representation of the life cycle of the benign tertian malaria 
parasite (Plasmodium vivax} in man and the mosquito. Nos. I to 4 show the growth of 
the parasite in the red blood cells; 5 and 6, the mature schizont dividing into merozoites, 
and their escape is shown in 7; these merozoites invade new red cells and the cycle con- 
tinues. Nos. 8, 9, and 10 show the development of the male and female gametocytes. The 
mosquito is shown obtaining these sex cells. No. u, the male cells (sperm) being dis- 
charged; 12, the sperm cell uniting with the female cell; 13, the fertilized zygotc; 14, the 
migrating egg or ookinete; 15, the oocyst outside the stomach wall of the mosquito; 16, a 
nearly mature oocyst; 17, the stomach of a mosquito showing oocysts; 18, the discharge of 
the sporozoites by the breaking of the oocyst; 19, sporozoites in the salivary gland; 20, the 
salivary glands of a mosquito; 21, an anophcline is seen discharging sporozoites into the 
blood stream of a new host; 22 to 28 show the asexual cycle in a new host. (Modified from 
James.) 



MOSQUITOES AND HUMAN WELFARE 337 

hours each schizont divides into a number, 12 to 24, merozoites and these are 
discharged into the blood stream by the rupturing of the cell wall (6 and 7). 
Along with the merozoites are liberated the wastes, pigments, and probably a 
toxin. Each merozoite now attacks a new red cell and, in about 40 hours, 
becomes a schizont, which divides, and liberates the merozoites at the end 
of about 48 hours. The escape of so many merozoites with their wastes cor- 
responds with the onset of a chill followed by a marked rise in the tempera- 
ture of the patient. Hence this type is known as the tertian or three-day 
fever, the chill and fever appearing on the third day. After the asexual cycle 
has continued for a number of days, there appears a new stage in the cycle 
of the parasite. Certain merozoites develop into male and female gameto- 
cytes or sex cells (8, 9, and 10). Two kinds are produced, male or micro- 
gametocytes and female or macrogametocytes. These now remain in the red 
blood cells and no further development takes place. 

At this point the anophcline mosquito becomes essential for the continuance 
of the life of the parasite. If a person having the micro- and macrogametocytes 
in his blood is bitten by a suitable anopheline mosquito (as Anopheles qua- 
drimaculatus) and numbers of these sex cells are obtained, a further remarkable 
development takes place in the stomach of the mosquito. The female or 
macrogamctocyte matures into what is called a macrogamete and is then ready 
for fertilization. The male cell or microgametocyte gives oil a number of small 
linear bodies, which are the true microgametes or male elements (n). These 
lash about till they find a macrogamete and one of them immediately pene- 
trates it (12) and completes the process of fertilization. The union of the male 
and female produces a zygote (13). The zygotes are produced in the stomach 
of the mosquito. The zygote, at first passive, soon elongates and begins active 
movement; hence it is called the ookinetc (14). The ookinete penetrates the 
wall of the stomach and establishes itself between the epithelial and muscular 
layers (15). Here it becomes spherical and grows very large by the absorption 
of food from the surrounding tissues. It is now called an oocyst (16). Within 
the oocyst remarkable changes (sporogony) take place and, at the end of four 
or five days, the oocyst is completely filled by very minute organisms, the 
sporozoites (18). The sporozoites escape by the bursting of the oocyst and are 
freed in the body cavity. As insects have no closed circulatory system, the 
blood bathing all the tissues, the sporozoites are now free to wander with the 
blood. They are said to bore into almost all the tissues and organs of the host, 
but great numbers of them invade the salivary glands (19). The sporozoites 
are now ready to be passed with the salivary secretion into a new host when 
the mosquito bites (21). The entire cycle (called the exogenous or extrinsic 



338 MEDICAL ENTOMOLOGY 

phase) within the mosquito occupies from 8 to 14 days or longer, depending 
on the temperature and other factors. It will thus be seen that the presence 
of anopheline mosquitoes is essential for the beginning of a new infection in 
man and furthermore that man with gametocytes in his blood is essential 
before mosquitoes can become infected. This interdependence, the so-called 
etiological chain of malaria, is well shown in Fig. 133. If this chain can be 
broken at any one point, a reduction or even a complete elimination of the 
disease can be accomplished. 

In the above account it would appear that the sporozoites discharged by 
the infected mosquito into the blood stream of a susceptible person invade 
the red cells directly and start the malaria cycle. This view has been generally 
held though the work on bird malarias has shown that such is not the case in 
those species causing diseases in birds. No observer has ever seen the direct inva- 
sion of red cells by sporozoites of human malarias. Shortt and Garnharn (1948) 
have demonstrated that in monkey malaria (Plasmodium cynomolgi) and 
human malaria (Plasmodium vivax) the sporozoites undergo a cyclical de- 
velopment in the parenchymatous cells of the liver. In P. vivax the sporozoites 
invade the liver cells and each sporozoite grows into an ovoid mass, forming 
a cyst. 1 Within each cyst the chromatic material (nucleus?) divides repeatedly 
and by the fifth to seventh day a fully mature schizont is formed, containing 
from 800 to 1000 merozoites. By the rupture of the schizont the merozoites 
escape; many of these reach the blood stream, invade the red blood cells, and 
start the blood cycle. Whether the developmental cycle of the sporozoites may 
occur in other tissues has not been determined. The sporozoite cycles for 
P. jalciparurn and P. malariac are still unknown. 

The blood cycles of the other species of malarial organisms correspond very 
closely to that of P. vivax. The time of sporulation differs that of P. malariac 
taking place at the end of three days and the rise of temperature occurring 
on the following day; that of P. jalciparurn taking place irregularly in from 
24 to 48 hours so that the rise in temperature of the patient is irregular; that 
of P. ovale is about the same as for P. vivax. Of course, people suffering from 
malaria may have two species present or a double infection of any one, and 
this complicates the clinical picture of the disease. 

In order that the exogenous phase of the malaria parasites may be com- 
pleted in a susceptible mosquito and the infected mosquito live long enough 
to transmit the infection, certain climatic conditions appear essential. With 
P. vivax the temperature must be over 62 F. (16.6 C.), optimum 77 F. 

1 New names, many of them, have been used to designate these stages but no uniformity 
has been reached. 



MOSQUITOES AND HUMAN WELFARE 



339 




340 MEDICAL ENTOMOLOGY 

(25 C.), and the relative humidity over 70 per cent; with P. jalciparum the 
temperature must be over 68 F. (20 C.), optimum 86 F. (30 C.) and the 
relative humidity at least 70 per cent. According to Gill (1938), vivax malaria 
can only maintain itself in temperate zones where the mean temperature dur- 
ing the hottest months of the year (July or August in the Northern hemisphere 
and January or February in the Southern hemisphere) lies between 60.8 F. 
(16 C.) and 68 F. (20 C.) or higher and where the mean monthly relative 
humidity does not fall below 70 per cent. For the malignant type (P. falci- 
parum) the temperature must be about or over 68 F. (20 C.), optimum 86 F. 
(30 C.), and the relative humidity near 70 per cent. Though these are not 
absolute values, yet, according to Gill (1938), they largely govern the distribu- 
tion of malaria though not the distribution of anopheline mosquitoes capable 
of transmitting malaria. Thus, in general, the global area where malaria may 
be endemic lies south of the summer isotherm of 60 F. in the Northern 
hemisphere and north of the 70 F. summer isotherm of the Southern hemi- 
sphere (Fig. 134) and in regions where temperature and relative humidity are 
such as to furnish suitable conditions for the completion of the exogenous cycle 
of the parasite and permit the mosquito to live long enough to infect new 
hosts. 

SOURCES OF ANOPHELINE INFECTIONS: In order that malaria 
may occur and maintain itself in any given region, certain conditions are 
essential. The climatic conditions must largely correspond to those outlined in 
the preceding paragraph. There must be persons who have in their blood the 
micro- and macrogametocytes of one or more of the malarial parasites; there 
must also be present a species of Anopheles that feeds on man and can act as a 
transmitter; and, finally, this anopheline must be present in reasonable num- 
bers to ensure adequate infection. The only known source of the gametocytes 
is man; no animal, either in the wild or under laboratory conditions, has yet 
been found in which the human malarial parasites can develop. There arc at 
least three types of human "carriers": (i) persons who have had the disease, 
recovered, and carry the gametocytes in their blood; (2) persons who have 
the parasites and gametocytes in their blood but have never sufTered clinical 
symptoms of the disease; and (3) persons who have the disease and continue 
to suffer relapses from time to time. The first two types are known as "latent" 
carriers and are a constant menace to the general population in any malarious 
region. The last type is probably as dangerous because, with the frequent 
recurrence of the disease, excessive numbers of the gametocytes may develop. 
Craig and Faust (1940) state that about 33 per cent of those having malignant 
malaria will carry gametocytes and hence are "carriers" while over 50 per cent 



MOSQUITOES AND HUMAN WELFARE 341 

of those with vivax malaria will normally be "carriers" with gametocytes in 
their blood. However, it has been demonstrated again and again that "carriers" 
with gametocytes in their blood may not infect susceptible mosquitoes while 
other "carriers" with only a few or nondcmonstrable gametocytes may infect 
anophelincs. The reason for this is not easy of explanation. 

Given a source of the parasites, the only other requirement for an outbreak 
of the disease is adequate numbers of a species of Anopheles which readily 
bites man and in which the sexual and sporogenous cycle can be completed. 
Not all human beings are good "carriers"; neither are all anophclines good 
transmitters of malaria. This condition is certainly fortunate, for if all our 
anophelines were good transmitters the difficulties in the reduction and control 
of malaria would be greatly enhanced. Unfortunately we do not know all the 
"good" transmitters or all the "poor" transmitters among the anophelines. 
Furthermore, it is well known that the same species of Anopheles may be a 
good or "dangerous" transmitter in one region (A. pseudopunctipennis in 
parts of Argentina and Mexico; A. subpicttts (rossi) and A. hyrcanus in the 
Dutch East Indies) and a poor transmitter of the disease in another region 
(A. pseudoptinctipennis in California; A. siibpicttis (rossi) and A. hyrcanus 
in British India). Table 7 based on all available literature gives the principal 
"good" or "dangerous" transmitters known from the world and the general 
region where they are known to transmit malaria. 

In Table 7 some species are recorded as "good" or "dangerous" transmitters 
of malaria either from known surveys or based on epidemiological grounds. 
About another score could be added, based on experimental infections under 
laboratory conditions or the finding of a few naturally infected forms in the 
wild. In North America the principal transmitters are A. qitadrimaculatus and 
A. freeborni. A. crucians is readily infected under laboratory conditions and 
undoubtedly acts as a transmitter in parts of its range. Though A. punctipennis, 
our most widely distributed species, is susceptible to infection, yet the role 
it plays in the spread of the disease is considered unimportant. A. atropos has 
recently been shown susceptible to infection and it probably acts as a transmitter 
within its range; A. waltyeri has been found infected in the wild and is readily 
infected under experimental conditions. 

NATURAL INFECTION IN ANOPHELINES: Based on an examina- 
tion of all available literature, nearly sixty different species or varieties of 
Anopheles have been recorded (from dissections) as having either gut or 
salivary gland infections (natural) . In order that malaria can exist in any region 
there must be present anopheline mosquitoes naturally infected with the 
parasites. If no such infections occur and if there are no human "carriers," 



342 



MEDICAL ENTOMOLOGY 



Table 7. The principal vectors of malaria throughout the world (52 species). 



North America north of Mexico 



Species 


Range 


Larval habitats 


A. jreeborni Aitken 


Southern Oregon, California 
in drier regions, New Mexico, 
western Texas 


Fresh seepages, irrigation 
ditches, rice fields, streams, in 
open sunlight 


A. quadrimaculatus 
Say 


Massachusetts west through 
Ontario to Minnesota south 
to central Texas, Gulf coast 
of Mexico, and east to Atlan- 
tic coast 


Lakes, ponds, lime sinks, im- 
pounded waters, fresh marshes, 
swamps, bayous, grassy pools, 
among driftwood, etc. Vegeta- 
tion usually abundant 



Mexico and Central America 



A. (N.) albimanus 
Wied. 


Southeastern Texas, through 
Mexico, Central America, to 
Colombia, Ecuador, and Ven- 
ezuela; the West Indies 


Pools, puddles, hoof prints, 
ponds, marshes, swamps, fresh 
or brackish lagoons, artificial 
containers, almost any kind of 
fresh water with exposure to 
sunlight 


A. (N.) aquasalis 
Curry 


Nicaragua, Panama, Trinidad, 
Lesser Antilles, northern Bra- 
zil to Alagoas 


Tidal marshes of rivers, brack- 
ish lagoons, irrigation waters 
(mostly along seacoasts in tidal 
areas) 


A. (Kertcszia) 
bellator D. & K. 
Important vector in 
Trinidad 


Trinidad, Venezuela 


Breeds only in water in epiphyt- 
ic bromeliads (especially "wild 
pineapples") 


A. (N,) darlingiRoot 


Mexico (Tabasco), Br. Hon- 
duras, Guatemala, Venezuela, 
south along Andean foothills 
to Argentina & Chile 


Fresh-water marshes, lagoons, 
seepages, overflows of rivers, 
streams, etc., with vegetation 
and exposed to sunlight 


A. (A.} pseudopunc- 
tipcnnis pseudopuncti- 
pennis Theo. 
Vector in parts of 
range 


California to Utah, east to 
great plains and south through 
Mexico, Central America, to 
Argentina and Chile 


Clean seepages, pools, im- 
pounded water, puddles, streams 
with algae; more or less open 
to sunlight 




South America 




A. (N.) albimanus 
Wied. 


See above 




A. (N.) albitarsis 
Lyn. Arrib. 
Vector in some parts 
of range 


Guatemala south through 
Central America to Paraguay; 
Trinidad 


In mats of aquatic vegetation 
in large ponds, marshes, la- 
goons, bayous of flooding riv- 
ers, and not too much shade 



MOSQUITOES AND HUMAN WELFARE 



343 



Species 


Range 


Larval habitats 


A. (N.) darlingi Root 


See above 


See above 


A. (M.) gambiae 
Giles 


Established in northeast Bra- 
zil; now exterminated (?) 


See below 


A. (A.) pseudopunc- 
tipcnnis pscudopuncti- 
pcnnis Thco. 


See above 


See above 


A. (N.) pcssoai 
Galvao & Lane 
Vector of malaria in 
the Amazon basin 


Colombia 
zil 


south through Bra- 


Open shallow pools with 
and algae 


grass 



Europe, North Africa, and the Near East 



(A. (A.} macitlipcn- 
nis complex) 
i. A. lahranchiae atro- 
parvus van Thiel 
Vector in England, 
Netherlands, Spain, 
Portugal, Germany & 
Siberia 


Widely distributed in Europe 
and Asia from England to 
Japan; from Sweden and mar- 
itime Siberia south to Spain 
and n.e. Italy; Mongolia 


Typically in brackish water 
along coastal areas but also oc- 
curs in fresh water inland as 
marshes, swamps, lagoons, and 
any suitable water more or less 
exposed to sunlight 


2. A. labranchiae la- 
branchiae Falleroni 
Vector in its range 


S. Spain, Italy, Dalmatian 
coast, Sicily, Sardinia, Cor- 
sica, n.w. coast of Africa 


Brackish water in coastal 
marshes, fresh water in rice 
fields, upland streams, and in 
many types of water 


3. A. (A.) mcssae 
Falleroni 
Vector in Romania & 
probably elsewhere 


From Norway and Sweden 
south to Italy & from Britain 
east to Black Sea and e. Siberia 


Cool fresh, standing bodies of 
water in large inland river val- 
leys, ponds, lakes, and marshes 


A. (A.) clavigcr Meig. 
(bijurcatus) 
Vector in Palestine 
and Syria 


Europe, Northern Africa, 
Turkestan, Asia Minor 


Marshes, rock pools, wells, cis- 
terns 


A. (M.) multicolor 
Cambouliu 
Vector on epidemio- 
logical grounds 


North Africa (desert areas), 
Egypt, Sudan, Cyprus, Ana- 
tolia, Palestine, e. Persia, Ba- 
luchistan 


Pools, stagnant or slow-flowing 
drains, shallow wells; pools 
fresh or saline; desert pools of 
high salinity 


A. (M.) pharoensis 
Theobald 
Vector in Nile prov- 
ince, Sudan 


Widespread in Africa, Mada- 
gascar, Palestine 


Swamps and rice fields with 
vegetation 


A. (A.} sacharovi 
Favr (elutus) 
Vector in Balkans, 
Palestine, Near East 


N.e. and central Italy, Sar- 
dinia, Corsica, Balkans, cen- 
tral Russia, east to west China, 
Iran, Iraq 


Coastal and inland marshes, 
fresh or brackish; seems to pre- 
fer sunlight 



344 



MEDICAL ENTOMOLOGY 
Table 7. Continued. 



Species 


Range 


Larval habitats 


A. (M.) serge nti 
Theobald 
Vector in Egypt & 
Palestine 


Canaries, Algeria, Tunisia, 
Egypt, Syria, Turkey, Pales- 
tine, n.w. India 


Rice fields, borrow pits, irriga- 
tion ditches, drains, seepages 


A. (M.) super pictus 
Grassi 
Vector in S. Europe, 
Mesopotamia, Balu- 
chistan 


Spain across southern Europe, 
Asia Minor, Syria, Palestine, 
to s.w. India 


Pools in hilly stream beds, riv- 
ers, irrigation water, seepages, 
all more or less open to the sun 



Africa mainly south of the Sahara Desert 



A. (M.) junestus 
Giles 
Vector throughout its 
range 


Throughout tropical Africa 
north into Ethiopia and south 
to Natal; Mauritius 


Swamps, weedy margins of 
streams & rivers, furrows, lakes, 
ponds, ditches, seepage areas 


A. (M.) gambiae Giles 
Vector in its range 

var. mclas Theo. 


Tropical Africa, Sudan north 
to southern Egypt, Arabia, 
Madagascar, Mauritius, Re- 
union 

More or less a coastal form 


Pools, hoofprints, puddles, seep- 
age, water holes, drains, pools 
in stream beds 

Both fresh and saline water 


A. (M.) hancoc^i Edw. 
Vector in its range, es- 
pecially when abundant 


Sierra Leone, Liberia, Nigeria, 
Cameroons, Belgian Congo, 
Uganda 


Grassy water holes, grassy 
ditches, native wells, streams, 
swamps 


A. (A/.) hargreavesi 
Evans 
Vector in its range, es- 
pecially when abundant 


Sierra Leone, Liberia, Gold 
Coast, s. Nigeria, Gaboon, 
Belgian Congo 


Among Pistia in open and jun- 
gle pools, swamps, stream mar- 
gins 


A. (M.) moucheti 
Evans 
Vector when in 
numbers 
var. nigeriensis Evans 
Vector when abundant 


Cameroons, central & eastern 
Belgian Congo, Uganda 

Southern Nigeria 


Grassy pools, margins of 
streams, swamps; vegetation 
usually present 

Clear water with Pistia, swamps 
among vegetation 


A. (M.) nili Theobald 
Heavily infected in 
nature 


Sierra Leone east to Sudan 
and south to Mozambique & 
Zululand 


Margins of streams in deep 
shade with vegetation; also in 
clean running water with little 
shade; swamps, ditches 


A. (M.) pharoensis 


See above 




A. (M.) pretoriensis 
Theobald 
Not considered im- 
portant 


Gold Coast across Africa to 
Somaliland south to Trans- 
vaal &c Natal; Aden 


Rock pools, scmistagnant pools 
in streams and ditches, shallow 
puddles, hoofprints; vegetation 
usually absent 



MOSQUITOES AND HUMAN WELFARE 



345 



Oriental Region 

(India, Ceylon, Burma, Malaya, China, Dutch East Indies, Philippines, 
and the other islands in this region) 



Species 


Range 


Larval habitats 


A. (A/.) aeon it us 
Doenitz 
(Feeds mainly on 
animals) 
Vector in Indo-CMna 


India, Ceylon, Burma, s. 
China, Malayan region, Neth. 
Indies, Borneo, Celebes, Phil- 
ippines; widely distributed 


Rice fields, streams, pools, 
drains, swamps, irrigation 
ditches, reservoirs, and similar 
situations 


A. (M.) cut id fades 
Giles 
Important vector in 
India, Ceylon 


Baluchistan to Burma south 
to Ceylon; also reported from 
Yunnan, Siam, Tonkin 


Pools, pits, wells, rice fields, 
pools in river beds, rock quar- 
ries, irrigation channels, slow- 
flowing streams; fresh water but 
tolerates brackish 


A. (M.) annularis v. 
d. Wulp 


India, Ceylon, Burma, s. 
China, Formosa, Siam, Indo- 
China, Malayan region, Neth. 
Indies, Philippines, Borneo 


Every type of water, pure or 
stagnant, contaminated; seep- 
ages, spring pools, flowing 
streams 


A. (M.) jhiviatilis 
James 
Vector throughout its 
range 


S. China, India, Burma, Siam, 
Turkestan, Baluchistan. Most- 
ly in foothills in its range 


Clean hill streams, pools in 
ravines, stream beds, irrigation 
channels, behind boulders in 
swift water, seepage holes; pre- 
fers sunlight 


//. (A.} hyrcanus 
sincnsis Wied. 
Known vector in 
China, s. Japan, Indo- 
China, Ned. Ind. 


N. c. India, Burma, China, 
Indo-China, Korea, Japan, 
Formosa 


Stagnant water of rice fields, 
pools, swamps, ponds, lakes, 
slow streams 


A, (M.) jcyporicnsis 
candidiensts Koidzurni 
Vector in Tonkin 

A. (A/.) jeyporicnsis 
jcyporicnsis James 
Not important vector 
in India 


India, China, Burma, For- 
mosa, Indo-China 

Eastern India and probably 
Indo-China 


Flowing water in ditches, seep- 
age water 

Flowing water in irrigation 
ditches, marshy edges of streams, 
lakes, and ponds 


A. (M.) Icucosphyrus 
Doenitz 
Vector in India, Bur- 
ma, Borneo, Neth. In- 
dies 


India, Ceylon, Burma, Ma- 
laya, Sumatra, Java, Borneo, 
Philippines, Indo-China 


Heavily shaded pools in beds of 
mountain streams, drains, ele- 
phant foot prints, wells; jungle 
breeder 


A. (A/.) maadatus 
Theobald 
Vector in Malaya, 
Netli. Indies, & As- 
sam (?) 


India, Ceylon, Burma, s. 
China, Siam, Malaya, Neth. 
Indies, Formosa, Philippines, 
Indo-China 


Pools in swift streams ob- 
structed by boulders, pools, rice 
fields, lake margins; prefers 
sunlight 



346 



MEDICAL ENTOMOLOGY 
Table 7. Continued. 



Species 


Range 


Larval habitats 


A. (A/.) minitnusTheo. 
Important vector in 
its range (Man is the 
preferred host) 


E. & n. India, Ceylon, Burma, 
Assam, Siam, Indo-China, s. 
China, Formosa 


Foothill streams, springs, irri- 
gation ditches, terraced rice 
fields, seepages; breeds in sun- 
light waters 


A. (M.) minimus fla- 
virostris (Ludlow) 
Vector in the Philip- 
pines 


Islands of the Philippine 
group, Celebes, Java 


As above for minimus 


A. (M.) mangy anus 
(Banks) 
Vector on epidemio- 
logical evidence 


Many islands of the Philip- 
pines 


Shallow, slow-flowing streams 
in or close to foothills, irriga- 
tion ditches, often in mats of 
vegetation; prefers sunlight 


A. (M.) philippinensis 
Ludlow 
Vector in Bengal; said 
not to be in the Philip- 
pines 


India, Burma, Malaya, Siam, 
Ncth. Indies, s. China, Philip- 
pines 


Tanks, pools, drains, rice fields, 
swamps, ditches, pits 


A. (M.) stephensi 
stephensi Liston 
Important vector in 
urban areas; impor- 
tant in its range 


Eastern Arabia, s. Iraq, Iran, 
India, Burma 


Wells, cisterns, flower pots, arti- 
ficial receptacles, roof gutters, 
temporary water 


A. (M.) subpictus 
Grassi 
Known vector in 
Celebes 


India, Malaya, Yunnan, Neth. 
Indies, New Guinea, Indo- 
China 


Borrow pits, buffalo wallows, 
brick pits, furrows in gardens, 
roof gutters; contaminated wa- 
ter, even brackish 


A. (M.) sundaicus 
(Rodenwaldt) 
Vector throughout its 
range 


India, Burma, Siam, Malaya, 
Sumatra, Java, Borneo, Les- 
ser Sunda Isls., s. Celebes 


Brackish or salt-water lagoons 
and swamps, pools of brackish 
water behind coastal embank- 
ments, tidal drains, and similar 
places 


A. (A/.) superplctus 
Grassi 


See above 




A. (A/.) umbrosus 
(Theobald) 
Vector in some areas 
of its range 


East India, Tonkin, Malaya, 
Coch in-China, Sumatra, Java, 
Borneo, Celebes 


Shaded stagnant pools & jungle 
morasses; (brackish water in 
mangrove swamps, =^ A. baezai 
Gater) 


A. (A.) barbirostris 
v.d. Wulp 
Not considered an 
important vector 


India, Ceylon, Burma, Siam, 
China, Malaya, Borneo, Su- 
matra, Java, Lesser Sundas, 
Celebes, New Guinea, Philip- 
pine Isl. 


Deep stagnant water with vege- 
tation and preferably in shade 
as margins of rivers, lakes, 
swamps, pools from springs, 
canals, rice fields, saline swamps 


A. (M.) kpchi Donitz 
Found infected in In- 
dia & Neth. Indies 


India, Burma, Malaya, s. 
China, Sumatra, Java, Borneo, 
Lesser Sundas, Philippines, 
Moluccas 


Small muddy pools, unplanted 
rice fields, streams, irrigation 
ditches, artificial containers 



MOSQUITOES AND HUMAN WELFARE 



347 



Australasian Region 



(Australia, Tasmania, New Zealand, Islands eastward to 180, New Guinea and 
islands north to equator and west to oriental region) 



Species 


Range 


Larval habitats 


//. (A/.) annulipesWlk. 
Only on epidemic- 
logical evidence 


Coastal and inland Australia, 
Tasmania, New Guinea. 
Breeds at elevations of 5000 ft. 


Grassy pools, edges of marshes, 
slow-running creeks, hoofprints, 
rock pools; at times in brackish 
water 


A. (A.} bancrojti Giles 
Found infected in 
New Guinea 


New Guinea, northern Aus- 
tralia 


Shallow water overgrown with 
vegetation in streams, and sim- 
ilar situations; prefers shade 


A. (A/.) jarauti La- 
veran 
Dominant vector in 
its range 


E. New Guinea, New Britain, 
Solomons, New Hebrides, n. 
Australia 


River & stream margins with 
vegetation, springs, wells, hog 
wallows, ruts, holes, hoofprints, 
ditches, and artificial receptacles 
as boats, tanks, drums, etc. 


A. (A/.) hmgae Belkin 
& Schlosser 
Vector in some parts 
as Guadalcanal (?) 


Guadalcanal 


In the jungle in seepage areas, 
potholes in streams, rock holes, 
dense jungle swamps, & tempo- 
rary pools 


A. (A/.) punctulatus 
Doenitz 
Vector in New Guinea 


Moluccas, New Guinea, New 
Ireland, Solomons, & adjacent 
islands 


Rain pools, road ruts, footprints, 
potholes in drying stream beds; 
pools may be muddy and free of 
vegetation; sunlight loving 



malaria will be absent despite the abundance of "good" or "dangerous" anophe- 
line transmitters. The introduction of human "carriers" is all that would be 
necessary for an outbreak of the disease. Boyd (1930) summarizes many of the 
dissections of anophelines made in order to determine the rate of natural 
infection. The results show a rather low "rate" of natural infection, though 
the rate must vary widely since it depends on many factors. In the United 
States, as summarized by Root, Anopheles quadrimaculatus shows a percentage 
infection of 1.47 (8864 dissections); A. punctipennis, 0.18 (543 dissections); 
and A. crucians, 0.25 (1203 dissections). King (1922, 1939) reports an infec- 
tion rate of 0.107 per cent (sporozoite) in 9340 dissections of A. quadrimacula- 
tus at Mound, Louisiana. In South America out of a dissection of 2666 A. albi- 
tarsis only 25 were found infected (all from Brazil). Causey, Deane, and Deane 
(1946) report a 10 per cent infection in A. gambiae found in houses and 5.6 
per cent in those taken in the wild, but Davis (1931) reports 62.8 per cent 
natural infections in 172 mosquitoes collected in houses at Natal, Brazil. In 
dissections of 7486 A. albimanus 53 were reported infected. A. darlingi has 
a high rate of infection from a maximum of 88.8 per cent in British Guiana 



348 MEDICAL ENTOMOLOGY 

(222 infected out of 250 dissected; Kenney, 1946) to as low as 1.8 per cent 
(1513 dissected; Deane, Causey and Deane, 1946). A. pseudopunctipennis 
showed 12 infected out of 435 dissected in Argentina (Davis, 1927), but Patter- 
son (1911) reported 1.03 per cent infection in 1549 dissections. Vargas et al. 
(1941) record 12 gut infections out of 526 dissections and 4 gland infections 
in 1246 dissections in Mexico. Downs et al. found 46 oocyst infections (3.3 
per cent) in 1383 A. aquasalis dissected (collected in houses in Trinidad) but 
out of 1364 only i with gland infection; in A. bdlator they record 10 stomach 
infections (0.78 percent) in 1263 dissections. In Africa A. jitnesttis varies in its 
infection rate from 3 per cent (20,000 dissected in Kenya; Garnham, 1938) to 
12.5 per cent at Freetown (Gordon, 1932). A. gambiae is reported by Gordon 
et al. (1932) to have an infection rate of over n per cent at Freetown. Barber 
and Olinger (1931) found 1798 infected out of 14,904 dissections (12.6 per cent 
made in Southern Nigeria. (The sporozoite rate varied from 2.2 to 30.5 per 
cent, according to the place where the mosquitoes were taken.) In Europe 
the main vector is A. maculipennis or its varieties. Dissections of this species 
show a low infection rate: in Macedonia 0.73 per cent in 14,713 dissections 
(Rice and Barber, 1935) and in Greek Macedonia 0.08 per cent (15,461 dis- 
sections) and a rate of 0.30 per cent in 1311 dissections of mosquitoes taken 
from one house on one day (Barber and Rice, 1937) . Swellengrcbel and de Buck 
(1938) report 5.58 per cent infected out of 44,167 dissections of A. nuicidi- 
pcnnis atroparvus (short wings) taken in houses in Holland but only i in- 
fected of A. macuhpennis mcssae (long wings) out of 2880 dissected. 

DURATION OF INFECTION IN THE MOSQUITO: How long the 
malarial parasites can survive in the salivary glands of mosquitoes has been 
partially determined in a number of instances. The ability of the sporozoitcs 
to survive for long periods and infect new hosts when the mosquito bites is of 
great importance. Mayne (1922), using Anopheles punctipennis infected with 
Plasmodium jalciparum, recovered the sporozoitcs (by staining) in the salivary 
glands for 68, 70, 71, 83, and 92 clays after infection. He produced infection in 
a human host by the bite of a mosquito that had been infected 55 days pre- 
viously. This same mosquito failed to infect on the 67th clay but dissection 
on the 68th day showed living sporozoites. Boyd et al. (1936) report that 
A. quadrimaculatus infected experimentally with P. jalciparum could transmit 
the disease for at least 40 days after the extrinsic developmental cycle; they 
proved valueless after 50 days. 

James and Shute (1926) kept batches of A. maculipennis infected with P. 
vivax at temperatures of 4 C. (37.4 F.) to 6 C. (42.8 F.) and these retained 
their infectivity for two and one-half months. James (1927) reports a group of 



MOSQUITOES AND HUMAN WELFARE 349 

A. maculipennis that retained infectivity for nearly six months; some of these 
were later reinfected and proved capable of transmitting malaria. Some of the 
reinfected specimens lived as long as three months after the reinfection. It has 
generally been assumed that malaria parasites cannot survive in the anopheline 
mosquitoes during hibernation, especially in the colder climates. King (1917) 
showed that P. vivax could survive in A. quadrimaculatus at a temperature 
of 30 F. ( 1 C.) for at least two days; at 31 F. for four days; and at a 
mean temperature of 46 F. (7.8 C.) for seventeen days. He also found that 
P. falciparum could resist temperatures as low as 35 F. (1.7 C.) for at least 
one day. 

James (1927) concludes from his observations on specimens of A. maculi- 
pennis that were infected with P. vivax and that remained infective for six 
weeks in spite of refrigeration at 3 to 6 C. that the tertian malaria organism 
might survive the winter in hibernating anophelines and thus produce pri- 
mary attacks of malaria in winter and early spring. Inasmuch as many anophe- 
line species in the north habitually seek out human habitations for the purpose 
of hibernation, there would seem to be no question that such individuals, if 
infected late in the autumn (natural infections are recorded from dissections 
as late as October 20 and November i, at Lenwil, Louisiana; October 4, at 
Mound, Louisiana; and October 25, at Edenton, North Carolina) could remain 
capable of infecting human hosts during the winter and early spring. Swellen- 
grebel and de Buck (1938) demonstrated that naturally infected A. maculi- 
pennis atroparvus in Holland lose their ability to transmit vivax malaria after 
December, for at that time the sporozoites are dead and there is no transmis- 
sion during winter and early spring, though this mosquito feeds on man during 
winter and spring. However, the temperature is below that required for the 
extrinsic cycle of the parasite. All the spring malaria consists of relapses (pri- 
mary) from infection received the preceding autumn. New infections occur 
only late in July to October when the temperature and relative humidity are 
right for the extrinsic development of the parasite. 

CONTROL OF MALARIA: The problem of malaria control consists 
in the breaking of the etiological chain at some vulnerable point. This could 
be done by any one of the following methods if we only knew some effective 
procedure: 

i. Elimination of the human "carriers." No very useful therapeutic measures 
are at present known by which the gametocytes can be destroyed in the 
circulating blood. Atebrine and quinine give indications of value; the new 
drugs paludrine, aralen, and pentaquine give some hope of success; and 
other drugs may yet be found, but it seems doubtful if such a beneficent drug 



350 MEDICAL ENTOMOLOGY 

can be discovered. This part of the etiological chain, then, remains unbroken. 

2. The successful treatment of malarial patients so as to effect a cure and 
prevent the formation of gametocytes. Quinine and its derivatives have been 
the standard treatments, but they do not completely cure or prevent the forma- 
tion of gametocytes. Atebrine, aralen, pentaquine, and paludrine are drugs of 
great value, but they are not perfect cures. Furthermore, if a successful treat- 
ment were known, this would not eliminate the first type of "latent" malarial 
carriers, though it would undoubtedly in time. 

3. Elimination of the anopheline transmitters. This is possible when we 
know more about anopheline biology and methods of control that are finan- 
cially practicable. This procedure would seem, at present at least, the most feasi- 
ble and, from experimental work so far carried out, the most efficient. For 
methods of control of mosquitoes see Chapter xn. 

Several palliative measures can be employed. These consist of effective screen- 
ing of malarial patients against anophelines and the use of screens and bed- 
nets by the general population in malarious regions. These measures, when 
adequately carried out, will greatly reduce the incidence of malaria. At the 
present time a combination of all these measures, however ineffective any one 
of them may be, is our best procedure in reducing the malarial scourge. 

BLACKWATER FEVER 

Blackwater fever is a severe fever of unknown etiology accompanied by 
prostrating chills, profuse vomiting, great destruction of the red cells (hemoly- 
sis), and the passage of hemoglobin in the urine (the urine is a mahog- 
any color, hence the name of the disease). At present it is apparently quite gen- 
erally accepted that blackwater fever is probably due to repeated attack or 
continuous infection with malaria. Apparently many cases develop during 
the treatment of malaria with quinine, and the administration of quinine 
may play some part in the genesis of the attack. The disease is widely distributed 
throughout the tropical and subtropical regions of the world and is most 
prevalent in the intensely malarious sections. In the Americas it occurs in 
the northern area of South America, the Central Americas, the West Indies, 
and parts of the southern states of the United States. Recently Stephens made 
an extended study of the incidence of this disease throughout the world and 
he shows that in the United States it has occurred in at least 18 states and 
as far north as New York, Illinois, Colorado, and California. Blackwater fever 
is a very severe disease with a high mortality. Apparently it can only be pre- 
vented by the avoidance of long and continued attacks of malaria. It has many 



MOSQUITOES AND HUMAN WELFARE 351 

complications and a person who has recovered from an attack should not 
continue to live in a highly malarious region. In order to reduce the incidence 
of the disease in any area the most logical procedure, based on our present 
knowledge of the disease, would be the destruction of malaria-carrying anophe- 
lines. 

YELLOW FEVER 

Yellow fever is one of the most virulent of human diseases. Until recently 
it was believed that the disease was of American origin and its transmitter, 
Aedes aegypti, an American species of mosquito. Accumulating evidence has 
definitely established the original home both of the disease and the mosquito 
to have been Central West Africa, whence they have been carried to the 
Americas. Though the mosquito has been carried by commerce to practically 
all regions of the globe where it can maintain itself, it does appear rather curious 
that the Americas became a permanent home of yellow fever. Carter in 1922 
gave the Caribbean littoral as the probable original home of the disease, but the 
same author in 1930 reached the conclusion, based both on historical and 
biological (very strong evidence) grounds, that Africa was the original home. 

DISTRIBUTION: At present yellow fever is widely distributed. It is 
known to be endemic in Brazil, the Amazon basin, Colombia, Venezuela, 
Peru, Bolivia, and probably other South American areas, and in Africa it 
extends from the west coast south of the Sahara into the Anglo-Egyptian Sudan, 
Uganda, Tanganyika, Ethiopia (?), and the great valley of the Niger. 

Formerly yellow fever was rather widespread around the Caribbean Sea 
and was introduced from time to time to northern cities, where numerous 
epidemics occurred during the summer. This disease, so highly fatal to non- 
immunes, remained a mystery till Reed, Carroll, Lazear, and Agramonte 
finally established, in 1900, that it could be transmitted from the sick to the 
well only by a mosquito, the tiger mosquito (Aedes jasciatus, Aedes argenteus, 
Stegomyia ]asciata, or Aedes aegypti; unfortunately this mosquito has a long 
list of synonyms). Their conclusions have been well established and the 
etiological chain in this disease is again the parasite (a virus), the man 
with the parasite (the patient), the mosquito, and finally a new patient. 
Noguchi isolated an organism, Leptospira icteroides, which he claimed was 
the etiological agent, but recent work has clearly shown that it is not that it 
is only Leptospira icterohaemorrhagiae ( interrogans), the causative agent 
of infectious jaundice (Weil's disease). The causative agent is a virus. 



352 MEDICAL ENTOMOLOGY 

Yellow fever is an acute, febrile, noncontagious disease, characterized by 
profound prostration, jaundice, hemorrhages, and albuminuria. The death 
rate is very high. A single attack confers immunity. The incubation period in 
man is generally three to seven days, though it may be shorter (two days) 
or somewhat prolonged (very rarely). However, the causative agent is nor- 
mally present in the blood stream of man only during the first three or four 
days after the onset of the disease. Whether it is present before the initial 
attack is still undetermined, though work with monkeys would indicate that 
it probably is. The period during which the parasite is present in the blood 
stream is of great significance when the infection of the mosquito carrier is 
considered. The importance of the mosquito in the spread of the disease may be 
stated very briefly. In order to obtain the parasite the mosquito (Aedes aegypti) 
must bite a patient during the first three or rarely four days after the initial 
attack. Within the mosquito the parasite undergoes a developmental cycle, 
for it is not till 9 (at temperatures of 28 C.) to 14 days later that the mosquito 
is capable of infecting a susceptible person. Once infected the mosquito re- 
mains capable of transmitting the disease to nonimmimes as long as it lives. 
How long an infected mosquito can live in nature is not easy to determine, but 
under experimental conditions infection has been transferred 59 days (one 
case), and 118 days (Hinclle, 1931) after the infecting meal. Bauer (1940) 
reports keeping an infected A. aegypti alive for 200 days. A single bite of an 
infected mosquito may bring about an attack of the disease. 

Until the year 1928 it was generally accepted jjiat^the yellow-fever chain 
consisted of the human patient (no other animals were known to be sus- 
ceptible), the yellow-fever mosquito (Aecles aegypti), and susceptible or non- 
immune human individuals. As there is no known specific treatment for the 
disease, all efforts were concentrated on the reduction or elimination of the 
mosquito in attempts to control yellow fever. So successful has this procedure 
been that practically the entire yellow-fever areas in the Americas have been 
rendered free from the disease. However, sporadic outbreaks, and these widely 
separated, have occurred and still occur in certain sections of South America. 
The endemic center in West Africa presented a problem and a serious menace 
as a possible focus for the continued spread of the disease. The investigations 
carried on at Lagos and at other African points have resulted in the re- 
examination of the entire yellow-fever problem. Stokes, Bauer, and Hudson 
(1928) for the first time demonstrated that monkeys (Macacus rhesus) were 
susceptible to the disease, producing fatal infections in two monkeys by the 
bites of Aedes aegypti 85 and 91 days after the mosquito obtained its infective 



MOSQUITOES AND HUMAN WELFARE 353 

blood meal. Since then a long list of different species of monkeys has been 
shown to be susceptible. In 1928 Bauer showed that other species of mosquitoes, 
Aedes stolen Evans (apicoannulatus Edw.), Aedes luteocephalus Newst., and 
Eretmapodites chrysogaster Graham, could act as transmitters of yellow fever. 
The results of Bauer's work have been fully confirmed and numerous investi- 
gations have since added other species of mosquitoes from various parts of the 
world. 

Yellow fever demonstrated its versatility when in 1933 Sopcr reported a 
jungle outbreak far from the presence of Aedes aegypti or any other known 
vector of the disease. Known now as "jungle yellow fever," it shows the same 
characteristics as the classical type (urban) but its source and all its vectors have 
yet to be determined. Those known at present arc listed below and the sus- 
pected animal reservoirs are indicated. The existence of jungle yellow fever 
will always be a menace, for an infected person or persons may visit the more 
distant urban centers (as by airplane) and form a focus for the infection of 
Acdcs aegypti (provided it is present in numbers). Jungle yellow fever is 
widespread in Africa. Recently Smithtuirn and Haddow (1946) reported the 
presence of yellow fever in mosquitoes taken from an uninhabited forest in 
Bwamba (Africa), indicating a cycle of yellow fever without the human 
factor. The development of a yellow-fever vaccine has been of inestimable value, 
for millions of people in yellow-fever areas can be readily vaccinated and 
immunity is of considerable permanence. 

These recent results show that the yellow-fever etiological chain is much 
more complicated than at first thought. There is an animal reservoir other than 
man and its extent is still unknown. Probably not all the mosquitoes capable 
of transmitting the disease have yet been discovered. In man it is generally 
stated that the virus occurs in the blood stream only during the first three or 
four clays after the initial attack. In susceptible monkeys it has been shown 
that the virus is present in the blood stream from the initial infection till their 
death and also in their tissues after death. By analogy it might be assumed that 
man has the virus in his blood shortly after the initial infection, that is, several 
days before the febrile attack. If true, the period during which mosquitoes can 
obtain the virus is increased. Again the old question as to whether there are 
"carriers" has been raised but it has not been finally answered. 

The following list presents data on the known mosquitoes that have been 
found capable of transmitting the disease from monkey to monkey or other 
experimental animals either by their bites or by a suspension of the ground-up 
bodies or that have been found infected in the wild: 



354 MEDICAL ENTOMOLOGY 

Table 8. Mosquitoes capable of transmitting yellow fever (excluding A. aegypti). 

*By bites, naturally. fExperimental transmission JFound infected in the wild. 
Efficient transmitters. by bites. 

1 1 Experimental transmission 
by crushed bodies. 



Africa (Ethiopian Region) 



Species 



General distribution 



Larval habitat 



}'Aedes aegypti 
queenslandensis 
(Theo.) 

%\Aedes afrlcanus 
(Theo.) 



^Aedes albopicttis Eastern Ethiopian, 

(Skusc) 

\\Acdcs initans 
(Theo.) 

*Aedes luteocephalus Widely distributed 
(Newst.) 

-\Aedes metallicus Widely distributed 

(Edw.) 

\\Aedes nigricephahts West African region 
(Theo.) 

\\Acdes punctocostalis West African region 
(Theo.) 



Eastern Ethiopian, Domestic, largely artificial con- 

northern Australia tamers 

Widespread Tree holes, banana stumps; oc- 

casionally in artificial containers. 
Adults tree-canopy-loving, crepus- 
cular 

Tree holes, rock holes, con- 
Oriental, northern Australia tainers; domestic 

Widely distributed Crab holes, brackish surface 

pools 

Tree holes, bamboo stumps 



*-\%Aedes slmpsoni 
(Theo.) 

* \Acdcs stol{esi 
Evans 

\Acdes taylorl 
Edw. 

\Aedes vittatus 
(Bigot) 

^Culex jatigans 
Wied. 

\\Culcx thalass'ms 
Theo. 

*-\-+Eretmapodites 
chrysogaster 
Graham 



Widely distributed 

West Africa, Uganda 
Nigeria, East Africa 



Tree holes, coconut shells 
Crab holes 

Not known. Probably ground 
forest pools (Hopkins, 1936) 

Leaf axils of banana, etc., pine- 
apple tops, tree holes, coconut 
shells. Adults diurnal 

Tree holes, banana and bamboo 
stumps 

Tree holes 



Widespread; also in Oriental Rock pools, drains, gutters, wells, 
and Australian regions and artificial containers 
about Mediterranean 

Widespread in tropics and Breeds in all sorts of pools, 
subtropics Domestic. 

Widespread Water holes, crab holes, earth 

drains, old pots 

Widely distributed Tree holes, fallen leaves, banana 

stumps, artificial containers 



MOSQUITOES AND HUMAN WELFARE 355 



Species 


General distribution 


Larval habitat 


* \Mansonia 
ajricanus 
(Theo.) 

^Mansonia 
unijormis 
(Theo.) 


Widely distributed and com- 
mon in tropical Africa 

Ethiopia, Orient, north 
Australia, n. & s. China, 
Formosa, Japan 


Larvae attached to aquatic plants 
Larvae attached to aquatic plants 



Neotropical and Nearctic Regions 
South America, Central America, West Indies, U.S.A. 



*^Acdes fluviatilis Brazil, Guianas Rock pools along rivers, ant 

(Lutz) rings, clay rings 

\\Acdcs ]ulvilhorax Trinidad, Surinam, Tree holes 

(Lutz) Venezuela, Brazil 

*\\Acdcs leucocelaenus Widely distributed Tree holes 

D. & S. 

\\Aedcsnubilns West Indies, Central and Temporary ground pools 

(Theo.) S. America 

\\Aedesscapularis Widespread Temporary rain pools 

(Rond.) 

\\Aedcsserratus Widespread Temporary rain pools 

(Theo.) 

\\Aedestaeniorhynchus Coastal areas, N., S., & Brackish pools or at times 
(Wied.) Central America, Mexico; fresh-water pools 

also inland marshes 

\\Acdcstcrrens Mexico, Central America, Tree-hole breeder 

Walk. to Argentina 

\Acdcs triseriatus North America Tree holes 

Say 

* \\Haemagogus Panama to Argentina Tree holes, bamboo stumps 

capricornii 
(Lutz) 

^Haemagogus Mexico to Argentina Tree holes 

cquinus Theo. 

*^$Haemagogus Colombia Tree holes, etc. 

spcgazzinii var. 
jalco Kum et al. 
(syn. janthinomys} 

^Haemagogus Colombia, Guianas, Tree holes 

splendent Will. Brazil 

\\Mansonia Brazil Attached to aquatic plants 

albicosta 
Pcry, 



356 



MEDICAL ENTOMOLOGY 
Table 8 Continued. 



Species 



General distribution 



Larval habitat 



\\Mansonia 
chrysonotum 
(Pery.) 

\\Mansonia 
jasciolata 
Lyn. Arrib. 

\\Mansonia 
justamansonia 
(Chagas) 

\\Mansonia 
titillans 
Walk. 

\\Psorophora cingulata 
Fabr. 

\\Psorophora jerox 
Hum. 

||Sabethines (pooled 

group) 

Sabcthoidcs 

Limatus 
Wyeomyia 

Gocldia 

Trichoprosopon 

\Acdes geniculatus 
(Oliv.) 



Brazil 



Attached to aquatic plants 



Mexico to Argentina Attached to aquatic plants 



Brazil, Colombia 



Neotropical 



Central America 
to Brazil 

Southern Canada to 
Argentina 



South American 



Attached to aquatic plants 

Attached to floating 
water plants 

Temporary rain pools 
Temporary rain pools 



Forest breeders 



Europe, Asia Minor Tree holes 



At present the number of known mosquitoes in which the parasite under- 
goes a cyclical development and can be transferred to susceptible animals is 17 
for Africa, 21 for South America, i for the Far East and i (Aedes aegypti) of 
general distribution, a total of 40 species. In addition other species have been 
somewhat incriminated by the inoculation of the infected macerated bodies 
into monkeys. Though this list is large, the importance of many of the species 
as transmitters of yellow fever to man is probably not great. Their chief sig- 
nificance lies in the fact that all of them are potential transmitters to monkeys 
or other susceptible animals that may become reservoirs of the virus. 

In addition to the above list of mosquitoes the following arthropods are 
capable of transmitting yellow fever, mechanically, through interrupted feed- 
ings: Stomoxys calcitrant, Ctenocephalides canis, Cimex lectularius and C. 
hemipterus (feces of these two also infective), Triatoma megista, Ornithodoros 
moubata, O. rostrata, Amblyomma cajennense, and other blood-feeding in- 
sects that attack man. 



MOSQUITOES AND HUMAN WELFARE 357 

ANIMAL RESERVOIRS: Man, suffering from yellow fever, was long 
assumed to be the only source for mosquito infection and the consequent 
spread of the disease. Since the discovery of Stokes and his co-workers (1928) 
that monkeys are susceptible to yellow fever, a rather long list of the monkeys 
of the Old and New World have been found susceptible. What this animal 
reservoir may mean in the future spread of the disease can only be conjectured. 
It clearly points to a serious condition should the disease reach India and the 
Far East. 

In the Old World many monkeys have been found susceptible: Macacus 
rhesus, M. cynomologus, M. sinicus, M. innus, M. nemestrinus, Cercopithecus 
tantalus, C. nicitans inpangae, Cercocebus torquatus, Erthrocebus patas, and 
many others; New World: Alonatta seniculus, Pithecia monacha, Cebus vane- 
gatus, C. versutus, C. flavus, Callithrix albicollis, C. penidllata (found infected 
in the wild), Leontoccbus ur stilus, Cebus macrocephala, Lagothrix lagotricha, 
Ateleus ater, Saimiri scireits, Pseiidoccbus azarae, and others. 

POSSIBLE SPREAD OF YELLOW FEVER: At present the transmitter 
par excellence, Acdcs aegypti, continues to breed almost unmolested in its 
range within the United States and probably also in many parts of Central 
and South America and the rest of the world. That yellow fever may spread 
again into regions where it has apparently been eliminated is not only a pos- 
sibility but a probability. With the development of airplane transportation, the 
most distant parts of the Americas are brought close to our doors. The intro- 
duction of a single incipient case or "carrier" (?) of yellow fever might be 
sufficient to start a small focus from which the disease could spread with great 
rapidity. Because of these possibilities, the elimination or reduction of Aedes 
acgypti should be attempted in all places where it now occurs. 

In 1932 the Rockefeller Foundation for Medical Research developed a vac- 
cine (a living, modified virus) that has proved of immense value in reducing 
outbreaks of yellow fever and bringing outbreaks under control. Since that 
year millions of people in yellow-fever areas and those going to such areas 
have been vaccinated. A single vaccination confers a longstanding immu- 
nity. 

DENGUE 

Dengue is a noncontagious infectious disease of low mortality. It is fre- 
quently known as "breakbone fever." Its onset is characterized by headache, 
aching eyes, and severe body and limb pains. The causative agent is unknown, 
but it is a filter-passing organism and is transmitted by mosquitoes. The disease 
is widespread throughout many tropical and subtropical regions of the world. 



35 8 MEDICAL ENTOMOLOGY 

It frequently occurs in epidemic or pandemic waves when the great majority 
of the population may suffer. Chandler and Rice (1923) state that the 1922 
epidemic in the United States was preceded by an excessive abundance of 
mosquitoes, especially Aedes aegypti. In Galveston and Houston there were 
over 60,000 cases, and some 500,000 to 600,000 cases were indicated from Texas 
alone. In Northern localities the disease appears in the summer or autumn 
when the mosquito host is prevalent, but it always dies out when cold weather 
intervenes, killing or? the mosquito. In North America dengue is confined 
largely south of 38 North latitude. 

Investigations of Siler and his co-workers (1926) and Simmons and his 
associates (1930 and 1931) prove that at least two species of mosquitoes, Aedes 
aegypti Linn, and Aedes albopictus Skuse, arc effective transmitters. Cleland, 
Bradley, and MacDonald (1906) had already proved that Aedes aegypti was 
an effective transmitter of dengue in Australia. The yellow-fever mosquito was 
undoubtedly first incriminated by Bancroft (1906). Culex jatigans (quinque- 
fasciatus), long considered an important transmitter, is now known not to 
play any significant part in its spread. Simmons (1931) confirmed the findings 
of Ashburn and Craig (1907) that by interrupted feedings Culex jatigans can, 
mechanically, transmit the disease and in epidemics may play a part in its 
spread. Furthermore, in Formosa, Armigeres obturbans has been shown capa- 
ble of transmitting the disease under experimental conditions. Recently Aedes 
scutellaris Walk, has been shown to be an important vector in New Guinea 
and New Hebrides. 

The virus of the disease appears to be present in the blood stream from the 
day before and during the first three or four days of the febrile attack. In order 
to become infected, the mosquito must bite a dengue patient during these first 
three to five days. It requires at least eleven (eight according to some workers) 
days before the mosquito is capable of transmitting the virus to a susceptible 
person. Once infected the mosquito remains infected throughout its life (70 
days experimentally for Aedes aegypti and 54 days for Aedes albopictus) . 

As in yellow fever, no experimental animals were formerly known to be 
susceptible to the disease. Recently Simmons and his associates (1931) have 
demonstrated that monkeys, Macacus fuscatus and M. philippinensis, are sus- 
ceptible, though they show no clinical symptoms. They proved the infection 
by transfers back by mosquitoes to human volunteers and other monkeys. 
They found that monkeys from nonendemic centers were more susceptible 
than those from regions where the disease is prevalent. It would thus appear 
that monkeys may be of considerable importance in the epidemiology of the 
disease. 



MOSQUITOES AND HUMAN WELFARE 359 

As many people suffering from this disease may have it in mild form, they 
remain at their daily tasks and are excellent subjects from which large num- 
bers of mosquitoes become infected. The yellow-fever mosquito is the most 
domesticated of all our species and it is present in large numbers in houses. It 
bites at all times during the day and even at night. It will thus be seen that 
a small outbreak may soon become epidemic and spread with great rapidity. 
The most efficient method of controlling the disease is by the elimination of 
the mosquito carriers. Aedes aegypti occurs throughout the tropical and sub- 
tropical regions, while Aedes albopictus, having about the same habits, is re- 
stricted at present to the Oriental region. It has been recently established in 
Hawaii. 

F1LARIASIS 

Filariasis is due to an infection with Wuchereria (Filaria) bancrofti Cobbold 
or W. malayi (Brug), rounclworms found in the adult stage in man. Filariasis 
is indigenous throughout a large part of the world and may be said to occur 
from about 41 North to about 30 South latitude in the Eastern hemisphere 
and from about 30 North to nearly 30 South latitude in the Western hemi- 
sphere. In the United States filariasis occurs only in a small area about Charles- 
ton, South Carolina, though at present it is practically extinct. 

WUCHERERIA BANCROFTI: The adult worms live together, often 
coiled up in tangles, in various parts of the lymphatic system. The females dis- 
charge their embryos in the lymph channels, whence they gain access to the 
blood stream. The embryos are generally known as micro filariae as they appear 
in the blood. Manson (1878) discovered that there was a marked periodicity 
in the appearance of the microfilariae in the peripheral blood, the maximum 
nocturnal abundance occurring between 10 P.M. and 2 A.M., while during the 
day they concentrated in the pulmonary vessels, capillaries of the heart, and 
parts of the kidney. This periodicity led Manson. to make his remarkable 
experiment with the house mosquito (Culex fatigans) and to discover the 
developmental cycle in the intermediate host, the first instance of an insect 
serving as an intermediate host of any parasite. 

Since the work of Manson, extensive studies in the Pacific area have shown 
there is also a nonperiodic strain of this filaria, the microfilariae being present 
in the blood stream of infected persons at all times during the day as well as at 
night. This condition occurs in the Philippines, Fiji, Samoa (where first dis- 
covered), Tahiti, and other islands in this region. However the filariae are 
identical with the periodic form known from the rest of the world. 



3 6o 



MEDICAL ENTOMOLOGY 




Fig. 135. (A} Microfilaria of Wuchcreria bancrojti in human blood. Nos. i, 3-6, 
8-12 illustrate the development of Wuchercria bancrojti by days in the mosquito. The 
last 4 days (13-16) are not shown because the worm becomes very large. (All photo- 
graphs from living specimens by R. J. Schlooser; all at the same magnification.) 



MOSQUITOES AND HUMAN WELFARE 361 

LIFE CYCLE IN THE MOSQUITO: When blood containing microfilariae (Fig, 
135 A) is obtained by a susceptible mosquito, the embryos escape from their 
sheaths and bore through the intestinal wall. In about 24 hours they have all 
migrated to the thoracic muscles. Here each worm undergoes further develop- 
ment (molting twice), but there is no increase in numbers. In from n to 20 days 
the larval development is complete and the parasites migrate forward to the pro- 
boscis. Finally they come to lie, generally in pairs, in the hemocele of the la- 




Fig. 136 (/<?//). Infective stage of Wuchcrerla bancrojti emerging h 
of a mosquito. (Photograph by R. J. Schlooser.) 
Fig. 137 (right}. Elephantiasis. Photograph of a case in Manilla. 

bium. They are now ready to pass to a new host. At the time of taking blood, 
the worms escape from the labium (Fig. 136) and are said to bore directly 
through the skin. In due time these larvae reach the lymphatics where they 
become sexually mature; eventually new generations of microfilariae reach 
the blood stream. The mosquito is an essential link in the chain in the develop- 
ment and transfer of this parasite. 

The presence of mature filarial worms in man does not necessarily mean a 
diseased condition. It is frequently associated with marked changes in the 
lymphatic system, however, and is believed to be responsible for a great variety 



362 



MEDICAL ENTOMOLOGY 



of organic disturbances, as lymphangitis, adenitis, elephantiasis (Fig. 137), and 
other complications. 

Since Manson's experiments a large number of mosquitoes have been dis- 
covered to act as intermediate hosts in the developmental cycle of this round- 
worm. Most of these discoveries have been made within recent years. The 
following list, though probably not complete, will give some idea of their 
numbers and distribution : 



Species 

Culex annulirostris Skuse 
Culex jatigans Wied. 

Culex juscanus Wied. 
Culex pipiens Linn. 

Culex pipiens pallens Coq. 
Culex tars ali s Coq. 
Culex ivhitmorei Giles 
Culex habilitator D. & K. 
Culex sinensis Theo. 
Culex tritaeniorhynchus Giles 
Culex salinarius Coq. 
Culex erraticus D. & K. 
Culex pallidothorax Theo. 
Culex vishnui Theo. 
Aedes aegypti Linn. 

Aedes pseudosci4tellaris Theo. 
Aedes scutellaris Walk. 
Aedes taeniorhynchus Wied. 
Aedes thibaulti D. & K. 
Aedes togoi Theo. 
Anopheles aconitus Donitz 



General distribution (as vectors) 
Dutch East Indies, Celebes 

Widespread in tropical and subtropical 
regions. Good vector 

China (Shanghai area) 

Widespread in temperate regions. (Vec- 
tor in China, Japan, Egypt; readily in- 
fected in U.S.A.) 

Central China, Japan 

Exp. in the United States 

East Indies and Pacific Islands 

West Indies 

Poor host in Australia 

Japan 

Exp. in the United States 

Exp. in the United States 

China, India, Ceylon, Siam, Indo-China 

India 

A good vector in some areas (West 
Africa, Dutch Guiana); not in others; 
not in the Pacific area 

Polynesia (Samoa area) 

New Guinea, New Hebrides, etc. 

West Indies (N., S., and C. America) 

Exp. in U.S.A. 

Japan 

Dutch East Indies 



MOSQUITOES AND 
Species 

Anopheles albimanus Wied. 
Anopheles albltarsis Lyn. Arrib. 
Anopheles algeriensis Theo. 
Anopheles am ictus Edw. 
Anopheles aquasalis Curry 
Anopheles bancrojtl Giles 
Anopheles barbirostris v.d.W. 
Anopheles constant Lav. 
Anopheles crucians Wied. 
Anopheles darlingi Root 
Anopheles jarautl Lav. 
Anopheles fuliginosus Giles 
Anopheles junestus Giles 
Anopheles gambiae Giles 
Anopheles hyrcanus nigerrimus Giles 
Anopheles hyrcanus sinensis Wied. 
Anopheles jeyporicnsis James 
Anopheles maculatus Theo. 
Anopheles maculipalpus Giles 
Anopheles minimus Theo. 
Anopheles pallid us Theo. 
Anopheles philippinensis Lud. 
Anopheles ramsayi Covell 
(pseudojamesi) 

Anopheles punctulatus Donitz 
Anopheles rhodesiensis Theo. 
Anopheles s pi en did us Koid. 
Anopheles squamosus Theo. 
Anopheles stephensi Listow. 
Anopheles subpictus Grassi 

( rossi Giles) 
Anopheles sundaicus Roden. 



HUMAN WELFARE 363 

General distribution (as vectors) 
Caribbean area 
Brazil 

Tunis (Africa) 
N. Queensland 
Brazil 

New Guinea (?) 
India, Celebes 
Mauritius 

America (poor vector) 
British Guiana 

Solomon Isls., New Hebrides 
India 
Africa 
Africa 
India 

China, Siam 
Hong Kong 
Hong Kong 
Mauritius 
Hong Kong 
India 
India 

India 

Solomon Isls., New Guinea 

Africa 

Hong Kong 

Sierra Leone 

India 

India 
India 



364 MEDICAL ENTOMOLOGY 

Species General distribution (as vectors) 

Anopheles varuna lyen. India 

Psorophora confinnis Lyn. Arrib. Exp. in U.S.A. 

Psorophora discolor Coq. Exp. in U.S.A. 

Mansonia ajricanus Theo. Africa 

Mansonia indianus Edw. Tonkin 

Mansonia juxtamansonius Chagas Brazil 

Mansonia pseudotitillans Theo. Malaya 

Mansonia unijormis Theo. Africa 

The above list (60 species) is rather long but it is not complete. In addition, 
some 45 species have been found refractory or not easily infected. Furthermore, 
many of the attempted infection experiments may have failed owing to the 
conditions under which they were performed. Basu and Rao (1939) demon- 
strated practically 100 per cent infection of Culex fatigans at temperatures of 
80 F. and relative humidity of 90 to 100 per cent; at temperatures of 60 F. 
or below and low humidity infection rarely occurred, or if it did the develop- 
mental period in the mosquito was greatly prolonged. 

No known drug has much efTect on this parasitic worm. Various operative 
measures are advocated but without great success. The only cilective method is 
the control of the mosquito transmitters in the various regions where filariasis 
is prevalent. Individuals in endemic areas should exercise great care to protect 
themselves from the bites of mosquitoes. Along with this should be considered 
the human carriers in order to reduce mosquito infection. 

Recently Brug (1927) described a new species of filaria, Wuchcreria malayi, 
from Sumatra. He has shown that nearly 50 per cent of the people are infected 
with this filarial worm and that it is transmitted by mosquitoes, Mansonia 
annulipes and M. annulata. He obtained 83 and 93 per cent infection in the 
mosquitoes in his experiments, while in nature he found i to 2 per cent infec- 
tion. Other known mosquito vectors include Mansonia annulifera, M. indianus, 
M. longipalpis (= annulipcs), M. unijormis, Anopheles barbirostris, and A. 
hyrcanus var. sinensis. At present this filaria is also known from other parts of 
the East Indies, New Guinea, Celebes, India, Indo-China, parts of China, and 
nearby regions. In Sumatra infection by this filarial worm results in a high 
percentage of elephantiasis. The life cycle of this worm in the mosquito is 
practically identical with that of W. bancrofti. 

Filariasis is not uncommon in many animals. Dogs suffer from a peculiar 
filariasis due to Diro filaria immitis. The adult worms are extremely long and 



MOSQUITOES AND HUMAN WELFARE 365 

slender and are found in the right heart or occasionally in the lungs. A number 
of mosquitoes serve as the intermediate host. The microfilariae do not undergo 
their development in the thoracic muscles but in the Malpighian tubules (Fig. 
63) of the mosquitoes. Hu (1931) lists seven Anopheles spp., seven Aedes spp., 
and three Culex spp. as known hosts in which development is completed. The 
North American species are Anopheles punctipennis, Aedes aegypti, A. cana- 
densis, A. sollicitans, A. taeniorhynchus, A. vexans, Culex pipiens, C. jatigans, 
C. restuans, and probably C. salinarius. 

Diroflaria magalhaesi is reported from man, one case in the left ventricle of 
a Brazilian child. Nothing is known of its development though, in all proba- 
bility, mosquitoes serve as intermediate hosts. Faust et al. (1939) report finding 
a Dirofilaria (a male) from a native of New Orleans, naming it D. lorn- 
sianensis. 

ENCEPHALITIDES 

A number of virus diseases have been generally grouped under this title. 
Of these virus diseases mosquitoes have been definitely proved as vectors of 
equine cncephalomyelitis (eastern and western strains in the United States and 
Canada and Venezuelan strain in Trinidad and northern S. America), St. 
Louis encephalitis (in middle and western United States), Japanese B en- 
cephalitis (Japan, Formosa, maritime area of China, and probably Siberia). 

EQUINE ENCEPHALOMYELITIS: This disease has long been known, 
under various names, as a highly fatal disease in horses. Meyer et al. (1931) 
first isolated the virus from sick horses in the San Joaquin Valley, California. 
In recent years thousands of horses in the United States have suffered from 
this disease (nearly 400,000 in the years 1935 to 1939) and many also in western 
Canada; the death rate varied from 30 to 90 per cent. In 1938 during an out- 
break of equine encephalomyelitis in Massachusetts human cases developed 
and were definitely established as caused by the virus of equine encephalomye- 
litis. In the same year human cases were also diagnosed in California. It is now 
established that in North America there are two strains, the western strain 
(occurs west of the Appalachian Mountain ranges) and the eastern strain 
(east of those mountains). Sporadic human cases were reported from various 
sections of the United States from 1938 till the great epidemic of 1941, when 
over 3000 human cases occurred in North and South Dakota, Minnesota, and 
the Canadian provinces of Manitoba and Saskatchewan (545 cases in this last 
province alone). From the beginning mosquitoes were suspected as vectors 
owing to their abundance and prevalence at the times and places of the out- 



366 



MEDICAL ENTOMOLOGY 



breaks. Experimentally Aedes aegypti was shown by Kelser (1933) to be easily 
infected by the western strain if fed on guinea pigs within two to three days 
after inoculation; there was an incubation period in the mosquito of at least 
six days. Soon a considerable number of mosquito species were shown experi- 
mentally to be capable of transmitting the disease, and the virus was shown to 
multiply in the mosquitoes. During the great human outbreak (1941) Culex 
tarsalis Coq. was found naturally infected in the Yakima Valley, Washington, 
by Hammon et al. (1941). Since then the following mosquito species have been 
found naturally infected : 



Species 
Culex tarsalis Coq. 



Culex pipiens Linn. 
Culiseta inornata Will. 



Disease 

Western strain 
(many times); St. 
Louis encephalitis 

Western and St. 
Louis encephalitis 

Western strain 



Anopheles jreeborni Aitken Western strain 
Aedes dor sails (Meig.) Western strain 

Mansonia perturbans (Walk.) Eastern strain 



Distribution and habits 
West of the Appalachian 
Mountains; breeds in all sorts 
of ground pools, containers; 
feeds on birds, man, etc. 

Widespread; breeds as above; 
feeds readily on birds, man. 

Widespread; breeds in more or 
less permanent woodland 
pools; bites man. 

Western N. America, west 
of the Rocky Mts. 
Widespread in northern U.S.; 
pool breeder, fresh or saline; 
bites man. 

Widely distributed, bites man. 
Found infected in Alabama. 
(Personal communication) 



At the present time no species of mosquito has been found naturally in- 
fected with the eastern strain. Experimentally the following species have been 
shown capable of transmitting either the western or eastern strain: Aedes 
aegypti (both strains), A. sollicitans (both strains), A. nigromaculis (western), 
A. dorsalis (western), A. taeniorhynchus (both strains), A. vexans (both 
strains), A. cantator (eastern), A. triseriatus (eastern), A. atropalpus (eastern). 
In addition the tick,-Dermacentor andersoni (western strain, transmission and 
transovarial transmission), the mite, Liponyssus sylviarum (western strain, 
natural infection in California), the chicken mite, Dermanyssus gallinae 
(western strain, natural infection), and the bug, Triatoma sanguisuga (strain ?, 
in Kansas) can transmit one of the strains. 



MOSQUITOES AND HUMAN WELFARE 367 

Venezuelan equine encephalomyelitis appears to be quite similar to the 
eastern strain of North America. Recently human cases have been reported 
from Trinidad. Gilyard (1944) reports the mosquitoes Aedes taeniorhynchus, 
Anopheles neomaculipalpis, and Mansonia titillans to be natural vectors. 

St. Louis encephalitis appears to be a strictly neurotropic virus. In 1933 and 
1937 extensive outbreaks occurred in St. Louis and the surrounding county. 
The virus was isolated in 1933 and proved to be a new virus. The outbreak 
of 1933 involved over 1000 human cases. The disease has now been reported 
from various parts of the western half of the United States. Hammon et al. 
(1941) isolated the virus from wild Culex tarsalis (captured in the Yakima 
Valley, Washington). This mosquito is known to be a definite vector. Culex 
pipiens has also been shown to be a vector. Smith et al. (1944, 1945, 1946, 
1948) have proved that Dermanyssus gallinae (the common chicken mite) is a 
natural vector among poultry and that there is transovarial transmission 
through generation after generation. This mite seems to be the natural reser- 
voir of the virus, infecting poultry and maintaining the disease. From infected 
birds mosquitoes obtain the virus and transmit it to other birds and ani- 
mals, including man. In addition, the dog tick, Derrnacentor variabdis, can 
transmit the virus in all stages and also through the egg. Hence this tick may 
also prove a good reservoir. The following mosquitoes have been shown 
capable of transmitting the virus of St. Louis encephalitis under experimental 
conditions or they have been found infected in nature: Culex pipiens, C. 
quinquejasciatus, C. tarsalis, Aedes aegypti, A. dorsalis, A. lateralis, A. nigro- 
maculis, A. taeniorhynchus, A. triseriatus, A. vexans, Anopheles jreeborni, 
A. punctipcnnis, Culiseta incident, and C. inornata. 

Japanese B encephalitis has been known from about 1871. In 1924 an exten- 
sive outbreak occurred in Japan and since then numerous cases have been 
recorded from those islands. Hsiao and Bohart (1946) report 12,341 cases 
between 1924 to 1933 with a death rate of 64.8 per cent. The disease has also 
been reported from Okinawa, where cases occurred among American troops 
as well as natives. From all available evidence mosquitoes are the vectors, and 
experimental transmission has been accomplished with Culex pipiens pallens, 
Culex tritaeniorhynchus, and Aedes to got. In Culex pipiens pallens there was 
successful transovarial transmission. The last species and C. tritaeniorhynchus 
were found infected in nature. 

RESERVOIRS OF ENCEPHALITIDES : It has been well established that 
the reservoirs of the eastern and western strains of equine encephalomyelitis and 
St. Louis encephalitis are primarily birds, especially domestic poultry. It will be 
noted that the mosquitoes concerned in the transmission of these diseases are 



368 MEDICAL ENTOMOLOGY 

well-known feeders on birds and also on man. Among birds the disease is 
undoubtedly transmitted by these mosquitoes, though the chicken mite, 
Dermanyssus gallinae, has been shown to be a most efficient transmitter among 
domestic fowls. The reservoir of the other one does not seem to be known. 

Rift Valley fever is a disease apparently restricted to parts of East Africa, 
particularly Kenya and Uganda. The virus of the disease was isolated in 1931, 
and in 1933 Daubney and Hudson demonstrated that mosquitoes (Mansonia 
spp.) were capable of transmitting the virus by inoculation (experimental). 
The disease occurs principally among sheep and cattle though goats, mice, 
and rats are susceptible. Monkeys are also known to be susceptible. During an 
outbreak in Kenya in 1944 humans, principally shepherds, became infected and 
laboratory personnel are reported to have contracted the disease. Smithburn 
et al. (1948) recovered the virus from a number of mosquitoes caught in the 
wild in Uganda. They report Acdcs tarsalis Newstead, A. albocephalus Edw., 
and A. dcndrophilus Edw. to be naturally infected. However the females of 
the first two species are not easily differentiated with certainty. Erctmapodites 
spp. were recovered infected in the wild several times, and E. chrysogaster 
Graham was shown to transmit the disease experimentally. 

MYIASIS (See Chapter xvn) 

Certain species of mosquitoes act as mechanical carriers of a human- and 
animal-myiasis-producing fly, Dermatobia hominis. For a full account see 
pages 517-521. 

BIRD MALARIA 

Species of the genus Culex are responsible for the transmission of bird 
malarias, rather common and widespread diseases of birds. 

FOWL POX 

Fowl pox, a common and widespread disease of poultry, has been shown 
(1928-1931) by several workers to be transmitted by a number of different 
species of mosquitoes. 

REDUCTION IN LAND VALUES 

It is common knowledge that an abundance of mosquitoes causes a marked 
reduction in land values. This is particularly true in summer, seaside, and lake 
resorts and in urban areas subject to mosquito invasion. Manufacturing and 
industrial districts often feel the effects of mosquito abundance. Some of our 



MOSQUITOES AND HUMAN WELFARE 369 

most valuable lands as in New Jersey and the bottom lands of Mississippi have 
had and continue to have their development retarded owing to hordes of 
mosquitoes, which frequently render life, except to the most hardened, unen- 
durable. When this is accompanied by diseases, the development is almost 
stopped. Furthermore, outbreaks of malaria and dengue throw another heavy 
burden on such communities due to sickness, the consequent loss of income, 
and the expense attendant thereto. The remarkable results following mosquito 
control and the consequent increase in real estate values and the health and 
vigor of the peoples have been noteworthy in many places but only a few 
can be cited, as Havana, Panama, the Canal Zone, Port Said, and Singapore. 
Where diseases are not present, but only noxious mosquitoes, the reduction 
of the latter brings about a marked increase in land values. No finer example 
can be cited than the work clone in New Jersey. Headlee (1926) after present- 
ing a detailed summary of the tax valuations of the Atlantic and Bay Coast 
area of New Jersey for the past twenty-five years concludes with this remarka- 
ble statement, "Thus it appears, under New Jersey conditions, that, where 
salt-marsh mosquitoes are naturally absent, there has occurred an average 
increase in taxable values during the past ten years of 55 per cent more than 
where they are still present or only recently reduced; and that, where salt- 
marsh mosquitoes have been largely eliminated during the last ten years, 
there has occurred an average annual increase of 75 per cent more than where 
they are still present or very recently reduced." 

REFERENCES 2 
MALARIA 

Barber, M. A., and Olinger, M. T. Studies on malaria in southern Nigeria. Ann. 

Trop. Med. Parasit., 25: 361-501, 1931. 
Boyd, M. F. Studies of the epidemiology of malaria in the coastal lowlands of 

Brazil. Amer. Jl. Hyg., Monograph 5, 1926. 

* . An introduction to nialariology. Cambridge, Mass., 1930. 

Carter, H. R. Report on malaria and anopheline mosquitoes in Ceylon. Colombo, 

Ceylon, 1927. Ceylon Sessional Paper, vn. 

Celli, A. A history of malaria in the Roman Campagna. London, 1933. 
Christophers, S. R. Malaria in war. Trans. Roy. Soc. Trop. Med. Hyg., 33: 277- 

292, 1939. 
*Covell, G. A critical review of the data recorded regarding the transmission of 

malaria by the different species of Anopheles; with notes on distribution, habits, 

and breeding places. Ind. Med. Res. Mem. No. 7, 1927. 

2 The literature on malaria is overwhelming; only a few references can be listed here; 
most references have long bibliographies and these should be consulted. 



370 MEDICAL ENTOMOLOGY 

**Covell, G. The present state of our knowledge regarding the transmission of 
malaria by the different species of anopheline mosquitoes. Rec. Mai. Surv. Ind., 
2: 1-48, 1931. 

** . Malaria control by anti-mosquito measures. London, 1931. 

*Craig, C. F. A manual of the parasitic Protozoa of man. New York, 1926. 

** , and Faust, E. C. Clinical parasitology. 3rd ed. Philadelphia, 1943. 

*Gill, C. A. The seasonal periodicity of malaria. London, 1938. 

**Hackett, L. W. The varieties of Anopheles maculipennis and their relation to 
the distribution of malaria in Europe. Kiv. di Malario., 14: 3-67, 1935. 

. Malaria in Europe. London, 1937. 

, and Missiroli, A. The natural disappearance of malaria in certain regions 

of Europe. Amer. Jl. Hyg., 13: 57-78, 1931. 

Hoffman, F. L. The malarial problem in peace and war. Newark, N.J., 1918. 

James, S. P. Malaria at home and abroad. London, 1920. 

. Epidemiological results of a laboratory study of malaria in England. Trans. 

Roy. Soc. Trop. Med. Hyg., 20: 143-165, 1926. 

. Report on the first results of laboratory work on malaria in England. Pub. 

League of Nations, iii, Health. (Review, Brit. Med. Jl., p. 79, July 10, 1926.) 

. History of a group of Anopheles mosquitoes infected with Plasmodium 

vivax (Grassi & Feletti). Abh. Gebiete Auslandsk., Hamburg Univ., 26, Ser. 
D (Med.): 220-222, 1927. 

. Problems of malaria prophylaxis. Conclusions of the Malaria Commis- 
sion of the League of Nations. Brit. Med. JL, ii, pp. 340-343, 1927. 

Jones, W. H. S. Malaria: a neglected factor in the history of Greece and Rome. 
Cambridge, Eng., 1907. 

. Malaria and Greek history. Manchester, 1909. 

King, W. V. The effect of cold upon malaria parasites in the mosquito host. 
Jl. Exp. Med., 25: 495-498, 1917. 

. On the development of malaria parasites in the mosquito. Amer. Jl. Hyg., 

10: 560-579, 1929. 

Kligler, I. J. The epidemiology and control of malaria in Palestine. Chicago, 
1930. 

*Knowles, R., and Senior- White, R. Malaria, its investigation and control. Cal- 
cutta, 1927. 

*Kumm, H. W. The geographical distribution of the malaria carrying mos- 
quitoes. Amer. Jl. Hyg., Monograph 10, 1929. 

*MacGregor, M. E. Mosquito surveys: a handbook for anti-malarial and anti- 
mosquito field workers. London, 1928. 

Malaria. Collected memoranda on the subject of malaria. Rec. Mai. Surv. Ind., 
i (2), 1930. (Reprints of selected papers from 1847 to 1924.) 

Pinto, C. Disseminac.ao da malaria pela avia^ao; biologia do Anopheles gamblae 
e outros anofelineos do Brasil. Mem. do Instit. Oswaldo Cruz, 34: 293-430, 1939. 

Ross, Ronald. The prevention of malaria. London, 1910. 



MOSQUITOES AND HUMAN WELFARE 371 

. Studies on malaria. London, 1928. 

Russell, P. F. Lessons in malariology from World War II. Amer. Jl. Trop. Med., 

26: 5-13, 1946. 
** , West, L. S., and Manwell, R. D. Practical malariology. Philadelphia, 

1946. 
Shortt, H. E., and Garnham, P. C. C. The pre-crythrocytic cycle of Plasmodium 

cynomolgi and Plasmodium vivax. Trans. Roy. Soc. Trop. Med. Hyg., 41: 785- 

795, 1948. 

. Demonstration of a persisting exo-erythrocytic cycle in Plasmodium cy- 
nomolgi and its bearing on the production of relapses. Brit. Med. Jl., i, pp. 1225- 

1228, 1948. 

Simmons, J. S., et al. Malaria in Panama. Amer. Jl. Hyg., Monograph 13, 1939. 
**Soper, F. L., and Wilson, D. B. Anopheles gambiae in Brazil, 1930-1940. The 

Rockefeller Foundation, N.Y., 1943. 
Swellengrebel, N. H., and de Buck, A. Malaria in the Netherlands. Amsterdam, 

1938. 
Watson, Malcolm. Prevention of malaria in the Federated Malay States. London, 

1921. 

YELLOW FEVER 

Bacot, A. W. Report of the Yellow Fever Commission (West Africa). Vol. 3 
(Suppl.). London, 1916. 

**Bates, M., and Roca-Garcia, M. Experiments with various Colombian mar- 
supials and primates in laboratory cycles of yellow fever. Amer. Jl. Trop. Med., 

26: 437~453 I94 6 - 
, and Roca-Garcia, M. The development of the virus of yellow fever in 

Hacmogogus mosquitoes. Ibid., pp. 585-605, 1946. 
Bauer, J. H. The transmission of yellow fever by mosquitoes other than Aedes 

acgypti. Ibid., 8: 261-282, 1928. 
, and Hudson, N. P. The incubation period of yellow fever in the mosquito. 

Jl. Exp. Med., 48: 147-153, 1928. 
Beeukes, H., Bauer, J. H., and Mahaffy, A. F. Yellow fever endemicity in West 

Africa. Amer. Jl. Trop. Med., 10: 305-333, 1930. 
Bugher, J. C., et al. Epidemiology of jungle yellow fever in eastern Colombia. 

Amer. Jl. Hyg., 39: 16-51, 1944. 
Carter, H. R. Immunity to yellow fever. Ann. Trop. Med. Parasit., 10: 153- 

164, 1916. 
* . Yellow fever. An epidemiological and historical study of its place of origin. 

Baltimore, 1931. 
Davis, N. C. Susceptibility of capuchin (Cebus) monkeys to yellow fever. Amer. 

Jl.Hyg., 11:321-334, 1930. 
. The transmission of yellow fever. Further experiments with monkeys 

of the New World. Amer. Jl. Trop. Med., u: 113-125, 1931. 



372 MEDICAL ENTOMOLOGY 

Davis, N. C., and Shannon, R. C. Further attempts to transmit yellow fever with 

mosquitoes of South America. Ibid., 14: 715-722, 1931. 
Finlay, Carlos E. Carlos Finlay and yellow fever. New York, 1940. 
Fosdick, R. B. Unraveling the yellow fever mystery. Rockefeller Foundation, 

a review for 1940, pp. 27-31. 
Garnham, P. C. C., ct al. The mosquitoes of the Kaimosi Forest, Kenya Colony, 

with special reference to yellow fever. Bull. Ent. Res., 36: 473-496, 1946. 
Gilmore, R. M. Mammalogy in an epidemiological study of jungle yellow fever in 

Brazil. Jl. Mammalogy, 24: 144-162, 1943. 
Kirk, R. An epidemic of yellow fever in the Nuba Mountains, Anglo-Egyptian 

Sudan. Ann. Trop. Med. Parasit., 35: 67-112, 1941. 
Kumm, H. W. The geographical distribution of the yellow fever vectors. Amer. 

Jl. Hyg., Monograph 12, 1931. 
, et al. Studies on mosquitoes of the genus Haemagogus in Colombia. Amer. 

Jl.Hyg.,43: 13-28, 1946. 

Lewis, D. J. Mosquitoes in relation to yellow fever in the Nuba Mountains, Anglo- 
Egyptian Sudan. Ann. Trop. Med. Parasit., 37: 65-76, 1943. 
** . General observations on mosquitoes in relation to yellow fever in the 

Anglo-Egyptian Sudan. Bull. Ent. Res., 37: 543-565, 1947. 
, Hughes, T. P., and Mahafify, A. F. Experimental transmission of yellow 

fever by three common species of mosquitoes from the Anglo-Egyptian Sudan. 

Ann. Trop. Med. Parasit., 36: 34-38, 1942. 
MahafTy, A. F., et al. Yellow fever in western Uganda. Trans. Roy. Soc. Trop. 

Med. Hyg., 36: 9-20, 1942. 

Philip, C. B. Studies on the transmission of experimental yellow fever by mos- 
quitoes other than Aedes. Amer. Jl. Trop. Med., 10: 1-16, 1930. 
Reed, W. The etiology of yellow fever. Phila. Med. Jl., 6: 790-796, 1900. 
Shannon, R. C., et al. Yellow fever virus in jungle mosquitoes. Science, 88: 

iio-in, 1938. 
Smithburn, K. C., and Haddow, A. J. Isolation of yellow fever virus from African 

mosquitoes. Amer. Jl. Trop. Med., 26: 261-271, 1946. 
*Soper, F. L. Jungle yellow fever. A new epidemiological entity in South 

America. Rev. Hyg. e Saude Publica, TO: 107-144, 1936. 
* . The newer epidemiology of yellow fever. Amer. Jl. Pub. Hlth. 27: 1-14, 

1937- 
Stokes, A., Bauer, J. H., and Hudson, N. P. The transmission of yellow fever to 

Macacus rhesus: preliminary note. Jl. Amer. Med. Assoc., 90: 253-254, 1928. 
, Bauer, J. H., and Hudson, N. P. Experimental transmission of yellow fever 

to animals. Amer. Jl. Trop. Med., 8: 103-164, 1928. 
**Taylor, R. M., and Cunha, J. F. da. An epidemiological study of jungle yellow 

fever in an endemic area in Brazil. I, II. Amer. Jl. Trop. Med., Suppl., 26, 

1946. 
Wadell, M. B., and Taylor, R. M. Studies on the cyclic passage of yellow fever 



MOSQUITOES AND HUMAN WELFARE 373 

virus in South American mammals and mosquitoes. Amer. Jl. Trop. Med., 25: 
225-230, 1945. 

Yellow Fever. Results of the work of Maj. Walter Reed, Medical Corps, United 
States Army, and the yellow fever Commission. . . . U.S. 6ist Congress, 3d 
Session, Senate Document 822. Washington, D.C., 1911. 

DENGUE 

Ashburn, P. M., and Craig, C. F. Experimental investigations regarding the 

etiology of dengue fever. Philip. Jl. Sci., B, 2: 93147, 1907. 
*Blanc, G., and Caminopetros, J. Recherches experimentales sur la dengue. Ann. 

Inst. Pasteur, 44: 367-436, 1930. 
Chandler, A. C., and Rice, Lee. Observations on the etiology of dengue fever. 

Amer. Jl. Trop. Med., 3: 233-262, 1923. 
Cleland, J. B., Bradley, B., and MacDonald, W. Dengue fever in Australia. 

Jl. Hyg., 16: 317-418, 1918; 18: 217-254, 1919. 
Mackerras, I. M. Transmission of dengue fever by Aedes (Stegomyia) scutellans 

Walk, in New Guinea. Trans. Roy. Soc. Trop. Med. Hyg., 40: 295-312, 1946. 
Perry, W. J. The dengue vector on New Caledonia, the New Hebrides, and the 

Solomon Islands. Amer. Jl. Trop. Med., 28: 253-259, 1948. 
Schule, P. A. Dengue fever. Ibid., 8: 203-213, 1928. 
*Siler, J. F., Hall, M. W., and Hitchens, A. P. Dengue; its history, epidemiology, 

mechanism of transmission, etiology, clinical manifestations, immunity, and 

prevention. Philip. Bur. Sci., Monograph 20, 1926. 
Simmons, J. S. Dengue fever. Amer. Jl. Trop. Med., n: 77-102, 1931. 
* , St. John, J. H., and Reynolds, F. H. Experimental studies of dengue, 

Philip. Jl. Sci., 44: 1-251, 1931. 
, et al. Transmission of dengue fever by Aedes albopictus Skuse. Philip. 

Jl. Sci., 41: 215-231, 1930. 
Usinger, R. L. Entomological phases of the recent dengue epidemic in Honolulu. 

U.S. Pub. Hlth. Repts., 59: 423-430, 1944. 

FILARIASIS 

Bahr, P. H. Filariasis and elephantiasis in Fiji. Jl. London Sch. Trop. Med., 

Suppl. i, 1912. 
Basu, B. C., and Rao, R. S. Studies on iilariasis. Ind. Jl. Med. Res., 27: 233-249, 

J 939- 
Brug, S. L., and Rook, H. de. Filariasis in Ned.-Ind. Geneesk. Tijd. Ned.-Ind., 

70:451-474,1930. 
*Buxton, P. A. Researches in Polynesia and Melanesia. London Sch. Hyg. Trop. 

Med., Mem. 2, 1928. 
, and Hopkins, G. H. E. Researches in Polynesia and Melanesia. Ibid., Mem. 

i, 1927. (Both reports beautifully illustrated.) 



374 MEDICAL ENTOMOLOGY 

Byrd, E. E., et al. Studies on filariasis in the Samoan area. U.S. Nav. Med. Bull., 

44: 1-20, 1945. 
Causey, O. R., et al. Studies on the incidence and transmission of filaria, 

Wuchererla bancrojti, in Belem, Brazil. Amer. Jl. Hyg., 41: 143-149, 1945. 
Coggeshall, L. T. Filariasis in servicemen: retrospect and prospect. Jl. Amer. 

Med. Assoc., 131: 8-12, 1946. 
Edwards, F. W. The carriers of Filaria bancrojti. Jl. Trop. Med. and Hyg., 

25: 168-170, 1922. 
Francis, E. Filariasis in southern United States. U.S. Pub. Hlth. Serv., Hyg. 

Lab., Bull. 117, 1919. 
*Feng, L. Anopheles hyrcanus var. sinensis Wied., transmitter of Wuchereria 

(Filaria) bancrojti in Woosung district Shanghai, China. Amer. Jl. Hyg., 14: 

502-514, 1931. 
Flu, P. C. Report on investigations in Surinam (South America), Sept. 1927 

to Dec. 1927. Acta Leidemsia, 3: 1-188, 1928. 
Giglioli, G. The transmission of Wuchereria bancrojti by Anopheles darlingi in 

the American tropics. Amer. Jl. Trop. Med., 28: 71-85, 1948. 
Heydon, G. M. Some common Queensland mosquitoes as intermediate hosts of 

Wuchereria bancrojti (Filaria bancrojti}. Parasitology, 23: 415-427, 1931. 
Hu, S. M. K. Studies on host relationships of Diro filaria immitis Leidy and its culi- 

cine intermediate hosts. Amer. Jl. Hyg., 14: 614-629, 1931. 
. Preliminary observations on the longevity of infective larvae of Wuchereria 

bancrojti in Culex pipiens var. pallens Coq. Chinese Med. JL, 49: 529-536, 

1935- 

. Experiments on repeated infections of filarial larvae in Culex pipiens var. 

pallens Coq. Ibid., 12: 13-18, 1937. 

. Studies on the susceptibility of Shanghai mosquitoes to experimental in- 
fection with Wuchereria bancrojti Cobbold. Peking Nat. Hist. Bull., 9: 249- 
260, 1935; 13: 39-52, 1938; 14: 15-22, 1939. 

Manson, Patrick. The filaria sanguinis hominis and certain new forms of parasitic 
diseases in India, China and warm countries. London, 1883. 

Menon, T. B., and Ramamurti, B. The behaviour of the infective larvae of 
Wuchereria bancrojti with special reference to their mode of escape and penetra- 
tion of the skin. Ind. Jl. Med. Res., 29: 393-401, 1941. 

Newton, W. L., and Pratt, I. Experiments to determine potential vectors of 
Wuchereria bancrojti in the continental United States. Amer. Jl. Trop. Med., 
26: 699-706, 1946. 

, Wright, W. H., and Pratt, I. Experiments to determine potential vectors 

of Wuchereria bancrojti in the continental United States. Ibid., 25: 253-261, 
1945. 

Taylor, A. W. The domestic mosquitoes of Gadau, Northern Nigeria, and their 
relation to malaria and filariasis. Ann. Trop. Med. Parasit., 24: 425-435, 1930. 



MOSQUITOES AND HUMAN WELFARE 375 

*Yamada, S. An experimental study on twenty-four species of Japanese mos- 
quitoes regarding their suitability as intermediate hosts of Filaria bancrojti 
Cobbold. Sci. Kept. Govt. Inst. Inf. Dis., 6: 559-622, 1928. 

ENCEPHALITIDES 

*Bishopp, F. C. Mosquito transmission of encephalomyelitis or brain fever of 

horses. Jl. Wash. Acad. Sci., 29: 495-501, 1939. 
Davis, W. E. A study of birds and mosquitoes as hosts for the virus of eastern 

equine encephalomyelitis. Amer. JL Hyg., 32: 45-59, 1940. 
Getting, V. A. Equine encephalomyelitis in Massachusetts. New Eng. Jl. Med., 

224: 999-1006, 1941. 
**Hammon, W. McD. The arthropod-borne virus encephalitides. Amer. Jl. 

Trop. Med., 28: 515-525, 1948, 

, and Reeves, W. C. Culex tar satis Coq., a proven vector of St. Louis en- 
cephalitis. Proc. Soc. Exp. Biol. Med., 51: 142, 1942. 
, and Reeves, W. C. Laboratory transmission of St. Louis encephalitis. Jl. 

Exp. Med., 78: 241, 1943. 
, et al. Isolation of the viruses of western equine and St. Louis encephalitis 

from Culcx tarsalis. Science, 94: 328-330, 1941. 
** , et al. Mosquito vectors and inapparent animal reservoirs of St. Louis 

and western equine encephalitis viruses. Amer. Jl. Pub. Hlth., 33: 201-207, 

1943. 
Leake, J. P. Epidemic of infectious encephalitis. U.S. Pub. Hlth. Repts., 56: 

1902-1905, 1941. 
Reeves, W. C., et al. Recovery of western equine encephalomyelitis virus from 

wild bird mites (Liponyssus sylvlarum) in Kern County, California. Science, 

105: 411-412, 1947. 
Rempel, J. G., et al. Multiple feeding habits of Saskatchewan mosquitoes. Canacl. 

Jl. Res., 24: 71-78, 1946. 
Smith, Margaret M., et al. St. Louis encephalitis infection of chicken mites, 

Dermanyssus gallinae, by feeding on chickens with viremia; transovarian pas- 
sage of virus into the second generation. Jl. Exp. Med., 84: 1-6, 1946. 
* , et al. Experiments on the role of the chicken mite, Dermanyssus gallinae, 

and the mosquito in the epidemiology of St. Louis encephalitis. Ibid., 87: 119- 

138, 1948. 

RIFT VALLEY FEVER 

Daubney, R., and Hudson, J. R. Rift Valley fever. East Afr. Med. JL, 10: 2-19, 

1933- 

Smithburn, K. C., Haddow, A. J., and Gillett, J. D. Rift Valley fever. Isola- 
tion of the virus from wild mosquitoes. Brit. Jl. Exp. Path., 29: 107-121, 1948. 



CHAPTER XII 



The Problem of 
Mosquito Control 



E preceding chapter has outlined briefly the important relations of 
JL mosquitoes to human welfare. Though these have been known for many 
years, only recently have somewhat adequate measures been taken to reduce 
mosquito abundance and then mainly in the control of disease-transmitting 
species. This is exemplified in the great antimosquito campaigns where special 
diseases had to be controlled in order that certain national developments could 
be undertaken or that wars could be prosecuted. The results of such under- 
takings have been of unprecedented success. Witness the work in the Malay 
Peninsula, Cuba, the Panama Canal Zone, New Jersey, parts of California, 
Italy, parts of Greece, Palestine, Singapore, the Tennessee Valley, and recently 
in the conduct of the Second World War and in the proposed extermination of 
malaria in the United States. All of these vast control operations have been 
organized by able men supported by governments or private capital in order 
that epidemic diseases might be brought under control so as to permit certain 
national developments. Yet despite this, vast areas of the most fertile regions 
of the world suiTer from mosquito-borne diseases which retard and, in some 
cases, prevent their agricultural and industrial development. Hoffman (1916) 
made a plea and presented a tentative plan for the eradication of malaria 
throughout the Western hemisphere. His plea was based on the knowledge 
"that malaria is perhaps the most important of human diseases, and though it 
is not often directly fatal, its wide prevalence in almost all warm climates 
produces an enormous amount of sickness and mortality." Boyd (1930) desig- 
nates malaria as "the worst of human scourges"; Russell (1943) estimates that 
even today there are 3,000,000 deaths each year from malaria and at least 
300,000,000 cases of malarial fevers annually throughout the world. 

The problem of mosquito control may be considered from two viewpoints. 
First is the reduction and control of species known to be good vectors of 



PROBLEM OF MOSQUITO CONTROL 377 

disease that is, species control or eradication. This is well illustrated by the 
work on yellow fever (urban) where the adequate control of Aedes aegypti 
will bring about the reduction and elimination of the disease. This, however, 
does not apply to jungle yellow fever, as we do not yet know all the complexes 
involved in control of this disease in jungle areas. Species control is also practical 
for dengue, for when A. aegypti, A. albopictus, and A. scutellaris are brought 
under control the disease usually disappears. This same procedure frequently 
applies to malaria. In our own country the control of Anopheles quadrimacu* 
latus would mean the elimination of malaria in our eastern and southern states 
provided no new vector reached our shores. An adequate demonstration of this 
procedure is well illustrated by the great reduction of malaria in parts of north- 
eastern Brazil by the control and eradication of the introduced vector Anophe- 
les gambiae. Many more examples could be given of the effectiveness of this 
procedure in controlling human disease by controlling the vector, or by what 
is called "breaking the chain" in the life cycle of the parasite or virus. How- 
ever, in the case of encephalitides, as St. Lou's encephalitis, eastern and western 
encephalitis, etc. the control of specific vectors is not easily possible, not only 
because we do not know all of them, but because it would be difficult to conduct 
a campaign directly against those we do know. So another procedure should 
be considered. In planning the control of a vector of a disease it should be 
decided whether all pest mosquitoes ought not also to be taken into account. 
When an insect-borne disease is prevalent, it is usually not difficult to arouse 
public opinion and obtain funds for adequate control work. When the epi- 
demic subsides the control operations are generally discontinued and mos- 
quitoes breed in abundance to plague the inhabitants. If full information in 
such a campaign is given that all mosquitoes should be controlled in order 
that the inhabitants may enjoy freedom from mosquitoes as well as the dis- 
ease, the good work can continue. This would increase the well-being of all 
and adequately provide against a future epidemic of the disease. 

In many sections, not only of our own country but in various parts of the 
world, a wise, well-organized, well-directed plan of mosquito (and of flies 
and other pest) control by cities, towns, counties, or other units would bring 
about a gradual reduction of these noxious insects, prevent the outbreak of 
disease, reduce or eliminate malaria, permit people to enjoy their gardens, 
playgrounds, parks, or other recreation facilities and so increase land and real 
estate values that the actual cost would be more than repaid by the increase 
in taxable values. In planning such work several fundamental facts must be 
borne in mind. In the first place, water should be considered one of the first 
essentials in any community and the proper handling of such a valuable and 



378 MEDICAL ENTOMOLOGY 

essential natural resource must be given first consideration. It is easy to elim- 
inate mosquito breeding if we eliminate all standing water, but such effective 
drainage might do more harm than good. How then shall such a problem be 
solved? In planning a control problem the area in which operations are to be 
conducted should be thoroughly studied and the following basic knowledge 
obtained : 

1. The mosquitoes breeding in the control area should be determined and 
all breeding places definitely located. 

2. The mosquitoes breeding outside the control area and that are liable to 
migrate should be investigated. This need not be an intensive survey but 
it should be careful enough to avoid sad experiences later when control activi- 
ties are under way. 

3. Topographical or aerial maps of the area should be obtained, and all 
mosquito-breeding places as well as all water areas such as ponds, wells, 
streams, lakes, and swimming pools should be carefully located on such 
maps. 

The three steps stated above are essential lo the outlining of control activi- 
ties. How can they be carried out? Successful control depends on scientific 
knowledge. Mosquitoes, either in the adult or larval stages, can be identified 
only by those who know them not by those who think they know them 
or believe that all mosquitoes have the same habits. In carrying out the first 
step much data may be obtained on breeding areas that can be located on 
the topographical map. But omitting all factors but the first one for the 
present, let us see the problem in its true relation to control. The species that 
is mainly responsible can usually be collected during an outbreak. If it 
proves to be the common house mosquito, Culex pipiens, the types of breed- 
ing grounds are well known, and certain control measures are indicated. If 
it proves to be Aedes vexans, a different breeding ground is assured, and 
other control measures must be applied. If the main outbreaks are due to 
the early spring species, as Aedes stimulant, A. excrucians, and A. fitchii, 
another type or types of breeding places must occur in or near the area. If 
anophelines are present in numbers, then still other types of breeding 
grounds prevail and other methods of control are indicated. If the main 
outbreaks are due to such migratory forms as Mansonia perturbans, Aedes 
vexans, A. sollicitans, A. cantator, or A. taeniorhynchus, the problem be- 
comes more complicated. 

The second step is necessary in order that the species breeding in the area 
surrounding the district under control may be known. If migratory species 



PROBLEM OF MOSQUITO CONTROL 379 

breed here, steps will have to be taken to reduce the breeding areas as much 
as possible. 

The third step may be combined to a great degree with the first if deter- 
minations are made from the larvae. Every part of the area should be care- 
fully mapped; all standing water, streams, ponds, cisterns, wells, catch 
basins, marshes, or lakes should be accurately located on a large-scale map. 1 
All such places, particularly the ponds, streams, bayous, swamps, etc., should 
be carefully described so that changes of personnel will not delay the work. 

When the above information is at hand, a definite plan for the ultimate 
reduction and elimination of breeding grounds may be undertaken. Any 
plan will depend largely on local conditions, the extent and character of the 
breeding grounds, and the species of mosquitoes involved. The only known 
methods now available are drainage operations, filling and grading, keeping 
the banks of streams and large ponds clear of marginal and floating vegetation, 
employment of surface-feeding fishes, oiling operations, and the use of 
poisons or the new remarkable insecticide, DDT. Any plans evolved should 
be in co-operation with all the other agencies which have to do with sanita- 
tion, city or rural planning commissions, departments of public works, etc., 
and such work should be under the immediate direction of the agency 
dealing with public health. It is too early yet to hope for states or provinces 
to undertake large-scale operations unless it is in particularly malarious 
regions and then only in co-operation with national governments. When 
the co-operation of all public bodies and the citizens of a given area can 
be obtained, plans should be carefully prepared and continuity of activity 
is essential from year to year. 

TYPES OF CONTROL OPERATIONS 

When a plan for mosquito reduction suitable for the area under con- 
sideration has been evolved, particular attention should be paid to the various 
methods of control. A few of these may be briefly outlined here. 

DRAINAGE 

When the known breeding areas are fairly well determined in a given 
district, those that can be drained or greatly reduced by drainage should 
receive the most careful consideration. Plans for drainage should be made by 

1 Such maps can be obtained by enlarging the topographical maps of the Geological 
Survey or aerial maps. 



380 MEDICAL ENTOMOLOGY 

expert sanitary or drainage engineers. Careful attention should be paid to 
the type of drainage, as open or closed drains, the grade of drainage, and 
the discharge of the flow. Where water has to be discharged from a diked 
tidal area, gates must be provided to prevent all backflow. This is true only 
if the land is to be reclaimed for agricultural or other developmental pur- 
poses. Otherwise open ditches with clean margins will permit the flushing 




Fig. 138. Vicksburg, Mississippi. Upper: Before malaria control drainage. 
Lower: After construction of reinforced concrete invert with sodded banks. 
(Courtesy Mr. Rector and Mississippi State Board of Health.) 

of these areas at each high tide. If the drainage is well done, all water will 
be carried away within a few days and thus prevent a brood of mosquitoes 
reaching maturity. Furthermore, the inflow of the tides will bring an abun- 
dance of fishes, which will aid in devouring any mosquito larvae present 
along the drains or that hatch with the presence of water. The problems of 
salt-marsh drainage, diking, pumping, and the maintenance of ditches, are 
all very difficult, but exceptional progress has been made in New Jersey 
and California. In the interior, where discharge into rivers, bayous, or lakes 



PROBLEM OF MOSQUITO CONTROL 381 

subject to rise in levels takes place, drainage gates should be installed. Various 
types are on the market, and full information can be obtained from engineer- 
ing firms. 

Drainage should be carried out only by experts. If well and carefully done 
(Fig. 138), the value of reclaimed lands, either for agricultural, develop- 
mental, or industrial purposes, will often more than repay the original cost. 
All drainage work must be carefully inspected from time to time in order 
that it be kept functioning properly. 

FILLING AND GRADING 

Filling and grading operations should be devej^ped as a continuous pro- 
cedure. Plans for this work can be made only when the mosquito-breeding 
areas are rdther definitely located, and the work should be done in co- 
operation with whatever organizations have supervision of public works 
park commissions, town- or city-planning commissions, building commis- 
sions, etc. In this way all temporary pools; stagnant and unsightly ponds; 
borrow pits; pools formed along railway embankments, by road or street 
construction, by building operations of all kinds, and by the impounding 
of water for city water supplies; and all operations of whatever kind that 
may bring about standing or stagnant water will be brought under the 
supervision of those in charge of mosquito-control work. By careful co- 
ordination of these various activities new ponds or pools may be avoided, 
and many old ones can be filled with the minimum amount of labor and 
cost. This feature of mosquito-control operations is one of the most impor- 
tant in cities, villages, and towns. Full authority by law should be provided 
for carrying out effectively the sanitary regulations involved in any or all 
such operations. 

STREAMS AND PERMANENT PONDS 

Local streams, rivers, and permanent and impounded bodies of water 
present many difficulties. Where the streams are sluggish and the banks 
have marginal vegetation, with little side pools, bayous, bottom lands sub- 
ject to overflow, etc., the problem becomes complicated. As far as possible, 
the stream should be diverted in a direct course with the maximum amount 
of fall. The vegetation and shrubbery should be removed but not so as to 
give an unsightly appearance. All rocks and debris that prevent a free flow 
or may provide stagnant pools during drought should be removed. Bot- 
tom lands subject to flood may be drained by subsoil drains. The control 



382 MEDICAL ENTOMOLOGY 

work along streams and rivers should be made as permanent as possible. 
In the case of large ponds or reservoirs that must not be drained, it is 
possible to reduce and even prevent mosquito breeding. Such bodies of water 
should have clear margins; the trees and shrubbery should be removed for 
some distance from the banks; flotage and the growth of all types of floating 




Fig. 739. Upper: A clean shore line where breeding of anophelines is practically elimi- 
nated. Lower: An area where it is practically impossible to obtain a clean shore line and 
breeding is abundant. (Wheeler Lake, Tennessee River.) 

vegetation should be prevented (Fig. 139). This will allow free wind action, 
which will largely prevent oviposition; the removal of the shrubbery de- 
stroys the resting and hiding places for the adults. This method of procedure 
has been found quite successful in some sections of Louisiana where stagnant 
water in bayous has been impounded by damming, raising the water level, 
clearing out debris, and removing the shrubbery. Here it was not possible 
to drain as the river level was higher than that of the bayous and pumping 



PROBLEM OF MOSQUITO CONTROL 383 

was not advisable, so the experiment of impounding these waters was tried 
and proved successful. This type of water storage should be attempted in 
other sections of the country. 

Local conditions create special problems, but as our knowledge of mos- 
quito biology increases, methods may be devised to prevent or control breed- 
ing. In many parts of the tropics the most hopeless situations have been 
valiantly attacked, and the results have been successful beyond the fondest 
hopes. It would therefore appear that even the most difficult situation in 
America can be successfully attacked if we have the courage and perseverance 
to push on to the end. 

IMPOUNDED WATERS 

The problem of mosquito control, particularly of anophelines that are ac- 
tive vectors of malaria, in areas where there has been extensive impoundage 
of water for power, flood or erosion control, or fish ponds has become a 
major one in many parts of the world as well as in our own country. Here the 
problem of water management is" *t>T great importance. Kiker and Strom- 
quist (1939) have laid down the essential requirements in the preparation 
of a reservoir for impoundage: "That the reservoir be cleared so as to present 
a clean water's surface after impoundage between maximum and minimum 
water levels; and that all depressions between maximum and minimum water 
levels be drained so as to provide water level fluctuation with the reservoir." 
When water is impounded in this manner, the problem of anopheiine control 
is greatly simplified. In addition to the usual control measures, outlined in 
the next few pages, a system of fluctuating water levels will show marked 
results in the reduction of mosquito breeding. During the breeding season 
the water level is lowered at regular intervals and then raised to within an 
inch or more of the previous level. The period of each fluctuation is usually 
about a week. This procedure may be called "cyclical fluctuation with water- 
level recession." By this method shore-line debris is stranded and marginal 
vegetation is largely prevented from gaining a foothold. The problems of 
marginal vegetation and debris are most important since such protected areas 
are ideal places for mosquito breeding. Until more is learned of the biology 
of shore-line aquatic and semiaquatic plants not much further progress can 
be made in the management of shore-line problems. The only thing that can 
be done on the basis of our present knowledge is to maintain clean shore 
lines (Fig. 139) by every available means as well as by water-level fluctuation 
and recession. 

When feasible it has been found advantageous to maintain high water 



384 MEDICAL ENTOMOLOGY 

levels, above the maximum "mosquito control" elevation, at the beginning 
of the growing season in order to delay the development of marginal vege- 
tation. This constant-level phase should be maintained until significant 
anopheline production begins. Such a procedure will prevent the seeds of 
some objectionable plants from gaining a foothold in the marginal areas 
and thus give a cleaner shore line later in the season when anopheline pro- 
duction is at its maximum. 

OILS AND OILING OPERATIONS 

Kerosene oil was one of the first oils suggested and used for the killing 
of mosquito larvae. It is still used and is very effective, but the film formed 
on the water surface is soon broken down, especially in warm climates. At 
present various grades of petroleum oils are extensively used throughout 
the world. In order to act effectively an oil should have the following quali- 
fications: (a) it should be highly toxic to larvae and pupae; (b) it should 
spread evenly and rapidly on all kinds of water; (c) it should penetrate 
through debris and vegetation; (cl) it should form a fairly stable and lasting 
film; (e) it should be noninjurious to man and not kill fish, waterfowl, or 
plant life; and (f) its cost should be reasonable. Such an oil is not easily 
obtainable, and various types are employed to meet the conditions under 
which they are used. 

How oils kill mosquito larvae is not very well understood. It is generally 
stated that the oil film is drawn into the tracheal system, and if the oil is of 
high volatility, the toxic action is very rapid owing to the penetration of the 
tissues. If the oil is of low volatility and viscosity, the death of the larvae and 
pupae is probably due to suffocation. 

After extensive investigations and field trials the New Jersey Experiment 
Station recommends an oil with the following qualities: type distillate fuel 
oil; gravity (A.P.I.) 27-33; flash 130 F. or higher; viscosity S.U. at 100 
F. 35 to 40; distillation 10 per cent at 43o-45o F., 50 per cent at 5io-55o 
F., 90 per cent at 630 F. and higher. This oil spreads well, will give a prac- 
tically perfect kill of larvae and pupae within a few hours after application, 
and leaves a fairly stable film. Under normal conditions the film will not last 
more than ten days to two weeks. This requires that fresh applications be 
made whenever breeding is observed. The amount of oil required varies ac- 
cording to the breeding area and the vegetation present. Twenty-five to sixty 
gallons will usually cover any given acre of water surface. 

Fuel oil as described above is rather objectionable on small ponds in pri- 
vate grounds, on fish ponds, on ponds containing aquatic ornamental plants, 



PROBLEM OF MOSQUITO CONTROL 385 

on ponds frequented by waterfowl, or in similar aquatic situations. To meet 
this objection the New Jersey Experiment Station devised a mixture of 
pyrethrum and oil known as the New Jersey Pyrethrum Mosquito Larvicide. 
It is composed of 66 per cent kerosene or similar light petroleum distillate; 
0.07 per cent pyrethrins; 33.5 per cent water; and 0.5 per cent sodium lauryl 
sulfate. This is a stock solution and is diluted i part to 10 parts of water 
before using. It kills larvae and pupae promptly, is not injurious to fish, plants, 
or waterfowl, but does not give any lasting film. 




Fig. 140. A shoulder spray tank used in spraying small ponds. (Courtesy 
Connecticut Agriculture Experiment Station.) 

In the Panama Canal Zone Curry (1943) reports most effective control of 
larvae and pupae by the use of ordinary bunker fuel oil as furnished by the 
United States Navy. The oil spreads well and kills promptly; the film is 
effective for about two weeks under the hot tropical sun. In general any good 
fuel oil is highly toxic to mosquito larvae. However, practically all these 
oils are not very effective on water heavily charged with sewage. 

The time of applying oil is of great importance. In many sections of the 
country where the early spring species are the chief menace the oil must be 
applied before the adults have emerged. Many of these species have only a 
single brood each season; hence the control measures must be carried out at 
the proper time. In sections of the country where there are several to many 
annual broods or where different species breed at different times the timing 



386 MEDICAL ENTOMOLOGY 

of the oiling operations is very important. Oil films break down in a short 
time, rarely lasting more than ten days to two weeks. In cooler climates the 
oil film is effective longer than in hot climates. Severe rainstorms may also 
affect the oil film. Careful inspection is essential to determine the timing and 
effectiveness of the oiling operations. 

The method of applying the oils will depend largely on the area to be 
covered, its accessibility to roadways, and the difficulties of actually reaching 
the water. On small ponds and streams, in wooded areas, in marshes, swamps, 
and similar places, the ordinary shoulder spray tank is most satisfactory 
(Fig. 140). Here the pressure is obtained by compressed air, and any size 




Fig. 141. A power sprayer used in oiling large areas accessible to 
roadways. (Courtesy Bergen County, New Jersey, Mosquito Commis- 
sion.) 

of nozzle may be used but preferably one that gives a fine mistlike spray. 
In areas accessible to trucks, as along roadways, extensive narrow marshes, 
or swamps, the oil may be applied from an auto truck having a tank and a 
pump driven by the engine of the truck (Fig. 141). Such power-driven spray 
outfits are in extensive use in orchards, parks, and woodland areas to control 
insect pests. They can easily be employed in antimosquito campaigns. By 
the use of several leads of hose, and lengthening them, extensive areas can 
be covered in a minimum time. Their use will depend entirely on local 
conditions and their availability. 

Many other methods of applying oil have been tried and some are in use. 
Streams, ditches, and ponds have been treated by placing barrels filled with 
oil above them, the barrels being so constructed that a constant drip reaches 



PROBLEM OF MOSQUITO CONTROL 387 

the surface of the water. The oil is gradually carried onward by the stream 
or spreads slowly over the surface. This is not very satisfactory owing to the 
failure of the oil film to penetrate the grassy margins, drift, or flotage. Waste 
soaked in oil and anchored in ponds has the same drawbacks. Fine sand 
soaked in oil and sowed broadcast over ponds has given satisfactory results. 
As the sand falls on the water or sinks through the vegetation to the water 
surface, the oil is given off and leaves a good film. 

In large lakes, ponds, and reservoirs, where the margin and flotage is not 
easily accessible except by small boats, a tank placed in a boat and fitted with 
a pump to give the necessary pressure may be employed (Fig. 142). The pump 




Fig. 142. Spraying a shore line with a petroleum oil mixture for mosquito control from 
a power boat. (Courtesy Tennessee Valley Authority, Division of Health.) 

may be used to force the oil out directly or it may be used to compress the 
air. If air compression is employed, pumping is not continuous and in gen- 
eral a better and more even spray may be obtained. 

In all oiling work the most essential points are the use of a good, free- 
running, toxic oil, good equipment, and extreme care in covering all the 
water surface with a film of oil. The laborers should be carefully trained 
and their work constantly supervised by reliable inspectors. 

POISONS 

In recent years poisons have been used extensively for the control of anophe- 
lines. As the larvae are surface feeders, any poison that will remain at the 
surface or on the surface film for a short time will be eaten by them. In this 
work Paris green has been found most efficient and has been employed ex- 



3 88 MEDICAL ENTOMOLOGY 

tensively in areas where malaria is endemic. The Paris greeri is diluted with a 
diluent such as soapstone, hydrated lime, or road dust and dusted on the 
surface by various means. When well done, the results are almost perfect, 
destroying practically 100 per cent of the anopheline larvae. More recently 
airplanes have been employed, which, carrying specially designed apparatus, 
have dusted large areas of marshes, swamps, densely wooded areas, lakes, 
and reservoirs with the greatest success. Only a pound to a pound and a half 
of Paris green need be used per acre. The most important problems in this 
work are to determine the correct diluent and the particle size of the Paris 
green in order that the dust may settle promptly and remain for some time 
on the surface film. In dusting either by hand or by airplane the work must 




Fig. 143. Airplane dusting with Paris green for the control of Anopheles larvae. 
(Courtesy Tennessee Valley Authority, Division of Health.) 

be done when there is no wind, usually in the early morning hours, or much 
of the material will be lost. Furthermore the pilots must be trained for low 
flying, 20 to 50 feet above the water surface (Fig. 143). As yet no successful 
way has been found to destroy the larvae of culicines by poisons, though much 
experimental work has been directed to this end. 

Recently it has been shown that borax, in concentrations of two to two and 
a half ounces per gallon of water, is effective in preventing mosquito breeding 
in rain-water barrels, cisterns, and similar containers. Borax-treated water 
should not be used for drinking purposes. It is excellent for washing purposes. 
The advantage of borax over oil is that it is permanent and needs only to be 
renewed when the cisterns, etc., are refilled by fresh water. Water barrels so 
treated have remained all summer without further treatment. It is only neces- 
sary to add more borax when the barrels are refilled by fresh rain water. 

Many other substances are under investigation, such as derris, pyrethrum 



PROBLEM OF MOSQUITO CONTROL 389 

powder, and other arsemcals, and methods of employing them against the 
non-surface-feeding culicines will undoubtedly develop. 

DDT AS A LARVICIDE 

During the Second World War a new insecticide appeared and received de- 
served attention. This is DDT or dichloro-diphenyl-trichloroethane or as 2,2-bis 
(/7-chlorophenyl) -i-i, i-trichloroethane. It is a white crystalline solid and was 
first produced in 1874 by Zeidler, a German chemist. Its melting point is 108 
to 109 C (226.4 to 228.2 F.). It is practically insoluble in water but dis- 
solves in many organic solvents as the following: 

Solvent Grams DDT in 100 cc. solvent 

Cyclohexanone 100 to 120 

Benzene 77 to 83 

Xylene 56 to 62 

Acetone 50 to 55 

Diesel oil No. 2 10 (approx.) 

Kerosene, crude 8 

Kerosene, refined 4 

Velsicol 20 --)- 

ir 
DDT has been experimented with in various forms by many workers in 

the United States, in war areas, and in other parts of the world. At present the 
following methods may be employed: 

1. A 0.5 per cent DDT in refined kerosene (water white) or Diesel oil No. 
2 at the rate of 0.05 pound per acre gave good control of larvae in Tennessee 
Valley Authority experiments. This would mean the application of about 
1.3 gallons of the mixture per acre. This preparation would require 4 pounds 
of DDT (pure) or 20 pounds (20 per cent DDT) to each 100 gallons 
of kerosene oil and it should be applied at the rate stated above. A 5 per cent 
petroleum oil solution may be prepared by dissolving 2 1 /s pounds of DDT in 
5 gallons of No. 2 fuel oil or kerosene oil. For treatment use only at the rate 
of 2 quarts per acre of water surface. The spray must be applied as a fine mist 
with slow delivery. 

2. A wettable DDT powder containing 50 per cent DDT could be used 
in the same proportions in ordinary water. This would require 8 pounds of 
the powder to each 100 gallons of water, but it should probably be applied 
at a higher rate as 2 to 5 gallons per acre. For culicine larvae these dosages 
should be increased about 2 times or slightly more. This form of DDT is 
usually referred to as a suspension. 

3. Water emulsions are prepared by dissolving DDT in one of the solvents 



39 o MEDICAL ENTOMOLOGY 

and adding a wetting agent or emulsifier to form a concentrate. One of the 
concentrates recommended is 25 pounds of DDT and 4 pounds of Triton 
X-ioo in 71 pounds of xylene. Dilutions are made by adding the required 
amount of the concentrate to water slowly, with continuous stirring. A 5 
per cent emulsion of DDT is prepared by adding i volume of the concentrate 
to 4 volumes of water or i volume of concentrate to 24 volumes of water for 
a i per cent emulsion and so on. As emulsions mix promptly with water, 
the effect of DDT on other aquatic organisms as Crustacea, fish, and aquatic 
insects other than mosquito larvae may be detrimental. At present the al- 
lowable amount of DDT to prevent damage is about o.i pound per acre of 
water surface. This would mean using about 2 gallons or less of a i per cent 
emulsion per acre so as not to exceed 0.05 p.p.m. of DDT in the water. In 
cisterns, wells, urns, or otiier containers the water of which is not used for 
drinking purposes the dosages should be increased to double or more and 
thus give more lasting control. 

4. DDT as an aerosol is handled by airplanes adapted for atomizing an oil 
solution of DDT. The solution (20 per cent DDT in Velsicol NR-70 as em- 
ployed by the Tennessee Valley Authority) is carried in the plane (Stearman 
17), and by means of pumps it is forced into a pipeline from the engine exhaust 
line (4-inch pipe) just in front of a standardized venturi so as to give a 
mistlike spray with droplets of 25 to 50 microns in size. By using such stand- 
ardized equipment an effective swath of 200 feet wide could be covered each 
trip by the plane, and this would give eflective control (about 90 per cent 
larval kill). The amount applied at each treatment was o.i pound per acre 
of water surface. Sixteen routine treatments in a single season over the same 
area gave excellent control of mosquito larvae and had no appreciable effect 
on fish food organisms (though most surface Hemiptera were destroyed). 
However, good results have been obtained by applying as little as 0.05 pound 
per acre of water surface. 

5. Many successful attachments for spraying DDT have been developed 
for various types of planes. For ordinary routine work involving considerable 
areas the Stearman 17 and various types of Army and Navy planes have 
proved very effective. The spray is delivered under pressure of about 100 
pounds per square inch by means of a pump and is delivered through a 
breaker bar placed on the underside of the lower wing on each side. Along 
each breaker bar are located a varying number of spray nozzles of the proper 
type to give the desired spray coverage. 2 Using such a plane a large area can 

2 The breaker bar has recently been largely replaced by a system of atomizing nozzles 
located along the trailing edge of the wings, or at outer corners of wings and tail. 



PROBLEM OF MOSQUITO CONTROL 391 

be covered with a highly concentrated DDT solution in very small amounts. 
The amounts applied per acre varies, but good results have been obtained by 
applying as little as o.i pound of DDT per acre as sprays (0.2 quarts of a 20 
per cent DDT solution). 

DDT AS AN ADULTICIDE 

The application of DDT solutions to the surface of buildings, both within 
and vvithout, have given good results in killing adult mosquitoes and other 
insects. As a result of numerous experiments the desired deposit (residual) 
to give adequate kill is about 200 milligrams of DDT per square foot. This 
is obtained by using a 5 per cent DDT solution in kerosene oil (5 pounds of 
DDT in i2/{> gallons of kerosene oil). To obtain r residue of 200 milligrams 
per square foot requires about i gallon of the 5 per cent mixture per 1000 
square feet. In applying the material a fine, not a mist, spray is required, and 
it should be under a pressure of 40 to 50 pounds so as to cover the surface 
without any runoff. Such a deposit when well applied will give adequate kill 
for over a month or longer. Such deposits can be obtained by the use of hand 
sprayers, knapsack sprayers, or power sprayers so long as adjustments are 
made to leave the proper amounts. This type of anopheline control has shown 
good reduction of malarial incidence in areas where extensive spraying of 
all buildings (on the inside) has been undertaken. More recently the wettable 
DDT suspensions have also given good kill of adults (mosquitoes and flies). 
The 50 per cent wettable DDT is usually employed only outside on gardens, 
shrubbery, trees, about bases of houses, and inside barns, chicken houses, and 
similar buildings. The wettable DDT gives good results when applied in- 
doors at concentrations of 5 to 12 pounds in 50 gallons of water, but usually 
leaves undesirable deposits in private homes. 

Aerosol bombs have been employed for some time for the killing of adult 
mosquitoes and flies. These bombs, in various sizes, are on the market and 
full directions for their use are stamped on each bomb. 

DDT FOR THE DESTRUCTION OF HIBERNATING ADULTS : 

Not much work has been done in this field owing to the difficulty of de- 
termining the main places of hibernation. However, Aitken (1946) describes 
such a treatment in an area of some 93 square miles in Italy. All the houses, 
barns, outbuildings, and places of shelter were thoroughly treated so as to 
give about 83 milligrams of DDT per square foot. The results indicated a 
marked decrease in anopheline breeding the year following treatment. There 
was also a recession of malaria from a splenic index of 43 per cent to 25 
per cent and a parasitemia from 21 per cent to i per cent. In an area where 



392 MEDICAL ENTOMOLOGY 

no such treatment was given the malaria index showed a marked increase. 
Soper et al. (1947) indicates somewhat similar results from the treatment 
of all buildings, etc., in an area of 120 square miles in the Tiber Delta, Italy. 
They used 6.5 per cent DDT in kerosene so as to leave about 200 milligrams 
of DDT per square foot of surface. This method should prove of value in 
areas where the main hibernating places of the anopheline carriers are mainly 
buildings of the local inhabitants. 

NATURAL ENEMIES AS CONTROLS 

Mosquitoes have many natural enemies, both as predators and parasites. 
Certain species of birds, bats, and insects prey upon them, but their effec- 
tiveness in reducing the mosquito population does not appear very marked. 
Many species of fish feed on the larvae and certain top-feeding fishes (min- 
nows, gold fishes, etc.) have been employed in attempts to reduce mosquito 
abundance. Gambusia affinis is probably one of the most valuable of top 
minnows as it is hardy, breeds rapidly, and normally frequents shallow water 
suitable for mosquito breeding. Gambusia holbroohj, a close relative of G. 
affinis, has been carefully studied by Hildebrand (1925) and his conclusions 
warrant the utilization of this species wherever it can be employed. His ex- 
periments covered a considerable range of aquatic environments, especially 
those with dense growths of water plants, and he found that Gambusia hol- 
broolft brought about a very marked decrease in mosquito breeding. In no 
single instance was the control perfect, but in certain experiments the results 
almost approached complete control. Gambusia affinis is a native minnow of 
the great Mississippi Valley; G. holbroofy, native to the Atlantic watershed; 
yet, despite their present wide distribution and abundance, reliance on mos- 
quito control by these fishes depends largely on introducing them into 
mosquito-breeding ponds, lakes, streams, etc., frequently each year. Further- 
more, in order that the fishes may do effective work, dense growths of aquatic 
vegetation must be prevented. The maintenance of top-minnow hatcheries is 
not difficult so that the costs of fish control are not high. Though G. affinis 
has been introduced into many parts of the world and striking successes have 
attended its introduction, yet too much hope must not be placed on fish as 
effective agents in mosquito control. As a natural aid they are extremely valu- 
able. Connor (1921) used, with remarkable effectiveness, the chalaco (Dormi- 
tator latifrons, family Gobiidae) in the campaign against yellow-fever mos- 
quito in Guayaquil, Ecuador. Here the city had no adequate water supply, 
the water being distributed daily to the householders and stored in tanks, 



PROBLEM OF MOSQUITO CONTROL 393 

cans, and other receptacles. As there were over 7000 tanks and 30,000 other 
types of water receptacles, the breeding of Aedes aegypti continued in great 
volume. As a modern water service could not be installed at once, Connor 
conceived the idea of using fish. After many trials he selected the chalaco and 
distributed at least one fish for every container. The fish, a local species, was 
obtained from fishermen and stored in a specially prepared well where con- 
ditions approximated those of the streams from which the fish came. In a 
few days the fish were transferred to a second well containing water similar 
to that used in the city. From the second well the fish were distributed to all 
water containers throughout the city. The results were remarkable, for 
mosquito breeding was reduced to a minimum. 

Many other species of top-feeding fishes have been employed and with 
considerable success. Though undoubtedly fishes play an important role in 
mosquito reduction and the utilization of certain species is highly to be com- 
mended, yet adequate control cannot be obtained by them alone unless the 
conditions are more or less ideal from the standpoint of the fishes employed. 
In any plan to use fishes in a control area, the best possible scientific advice 
should be obtained. The effectiveness of the fishes depends on conditions 
which bring about their rapid breeding and maintenance and furnish them a 
continuing food supply. 

OTHER METHODS OF MOSQUITO REDUCTION 

In recent years much attention has been devoted to the study of the aquatic 
conditions that favor or reduce mosquito breeding. It is a common observation 
that certain ponds, etc., are favorite breeding grounds while in other similar 
ponds or marshes no breeding occurs. Though much work has been done, 
no definite conclusions seem warranted. Certain aquatic plants as Cham and 
Phyllotria species appear to have a deterrent effect both on egg deposition 
and larval development. Other plants, as Utricularia spp. (Fig. 144, bladder- 
worts) destroy large numbers of larvae (Matheson, 1931) though Hildebrandt 
(1925) concluded that U. macrorhiza (= vulgarii) and U. radiata had very 
little effect in reducing larval abundance in ponds that he observed in the 
southeastern states; surface-loving plants as species of Lemna, Wollfia (Fig. 
144), and Azolla form dense mats on the water surface and prevent egg de- 
position or interfere with larval development; and other plants may play 
important roles in the prevention of breeding or encourage excessive abun- 
dance of larvae. In general it may be said that the presence or absence of the 
necessary larval food appears to be the deciding factor. But what is the 



394 MEDICAL ENTOMOLOGY 

necessary larval food? Many examinations of the larval gut contents have 
been made; some studies of the plankton in typical breeding pools versus 
nonbreeding pools have been carried out; from these, however, no conclusions 
can yet be drawn. As the larvae sweep all available material into their intesti- 
nal tracts, there is no means of deciding what is actually digested and what 
is passed out in the wastes. Hinman (1930) has shown that a large proportion 
of the material ingested by the larvae passes through the alimentary canal 




Fig. 144. Left: Portion of stem of bladderwort (Utricularia) with mosquito larvae in 
four bladders. Right: Surface of water completely covered by Wollfia punctata and a 
few plants of Lemna minor. 

unchanged and thus cannot be regarded as food. He further demonstrated 
that larvae of Aedes aegypti can be reared under sterile conditions. Eggs, 
sterilized externally, were introduced into Berkefeld-filtered water, and nor- 
mal adults emerged in eight to nine days (the usual time under the most 
favorable conditions). The only food available for these larvae was the 
solutes and colloids that could pass through the finest filters. Matheson and 
Hinman (1931) also demonstrated that larvae of several other species of 
mosquitoes grew vigorously in Berkefeld-filtered water. It would seem clear, 
then, that probably the most important sources of foods for mosquito larvae 
are the substances in solution and colloids present in the water. If we could 



PROBLEM OF MOSQUITO CONTROL 395 

determine what are the essential solutes, considerable progress might be made 
in simplifying the problem of mosquito control. If by the use of certain 
aquatic plants, by the chemical treatment of water areas, etc., the necessary 
larval food can be destroyed, mosquito control operations may be greatly 
simplified and rendered less expensive. 

PROTECTION FROM MOSQUITOES 
SCREENING 

Though actual control measures against both larvae and adults of mos- 
quitoes may be carried on in any locality, probably the most effective measure 
to ensure comfort in homes is by screening. Screening not only effectively bars 
mosquitoes but also eliminates many other noxious insects as houseflies, 
black flies, and others. In all populated areas where financial means are ade- 
quate screening should be practiced. In areas where housing is poor, financial 
means are not available, and the population is indifferent, every effort should 
be made to aid such communities. It has been definitely proved that adequate 
screening, even in highly malarious rural areas with inadequate housing, 
will reduce malaria to a minimum. Screening should be well done so that 
no entrances are left, such as through open fireplaces or openings in flooring 
or walls. Porches should also be screened. Such screening combined with 
DDT treatments (residual sprays) of the interior and screens will ensure 
comfort in homes. The type of screening wire will depend largely on the 
locality and the availability of material. In general the i6-mesh screen (16 
meshes to the inch) will prove most useful. Copper, bronze, or galvanized 
screens are available and recently plastic screens -have been developed. Cop- 
per or bronze screens are long lasting, even in areas near the sea, while 
galvanized screens may give only a few years' service and then must be 
repaired or renewed. Full details of methods of screening will be found in 
the references. 

PERSONAL PROTECTION 

When traveling or living in areas where there are dangerous insect-borne 
diseases (malaria, yellow fever, filariasis, dengue, etc.) bed nets should be a 
part of the equipment. These are available or may be made. In entering a bed 
net great care should be exercised to see that all mosquitoes or other insects 
are absent or are killed. The bed net should be carefuly tucked about the bed 
or sleeping place so as to leave no opening, and the net should be so arranged 
that the sleeper's body does not touch the net at any point. 



396 MEDICAL ENTOMOLOGY 

During World War II excellent mosquito repellents were developed and 
tested. These consist of Rutgers 612 (2-ethylhexanediol-i-3), dimethyl phthal- 
ate, and indalone. They are available and give a fair degree of protection 
against mosquitoes and black flies. For general protection against insects a 
combination of the three is recommended, i.e., 6 parts of dimethyl phthalate, 
2 parts of Rutgers 612, and 2 parts of indalone (the so-called "6-2-2" formula). 
These materials should be applied according to the directions of the manufac- 
turer. They are not injurious to the skin and should be rubbed over all ex- 
posed surfaces, but avoid getting them into the eyes. Alone or in combination 
they will give fairly good protection for two to four hours. They can also be 
rubbed or spread over the clothing with impunity and thus give added 
protection. 

SPECIAL CONTROL PROBLEMS 

The general methods of mosquito control have been outlined above. 
Several special phases need to be emphasized. These concern the control of 
yellow fever, malaria, and dengue. Though yellow fever is now known to 
be transmitted (at least from monkey to monkey and probably from man to 
man, or monkey to man) by many species of mosquitoes in addition to the 
yellow-fever mosquito (Aedes aegyptt), the transmitter that must be con- 
sidered of prime importance is the last one. Furthermore, an animal reservoir 
of at least vast possibilities has been discovered in a large number of different 
species of monkeys. At present the disease is restricted to extensive areas in 
South America and a large area in West Africa extending deep into the 
continent. Formerly it was thought that if the disease in man could be 
stamped out, either by the death of the infected or their recovery (immunes), 
no further centers of infection would exist so that the presence of the yellow- 
fever mosquito would no longer be a menace unless new human cases were 
brought in from other centers of infection. Also the mosquito transmitter 
(Aedes aegypti) was looked upon as an urban mosquito, not common or 
abundant in rural areas. Whether this conclusion can be accepted as fully 
proved is doubtful. That this mosquito does not occur far from human habita- 
tion appears well authenticated, and there seems no reason to doubt that it 
could become established about every human abode where it can survive. 
Given these conditions and the presence of monkey reservoirs, it would seem 
that the possibility of permanent yellow-fever centers is assured. Though 
an excellent vaccine is now available and most effective, it would be an en- 
tirely justified procedure for all cities, villages, towns, and other centers of 
population seriously to plan a strict control over this mosquito. If not, an 



PROBLEM OF MOSQUITO CONTROL 397 

outbreak of yellow fever involves almost a military supervision (as in the 
outbreaks in New Orleans, Rio de Janeiro, etc.). As this mosquito breeds 
practically only in artificial water containers, the consistent and continued 
elimination of these breeding places would result in such a permanent reduc- 
tion of the numbers of this mosquito that the introduction of a few yellow- 
fever cases would not result in an outbreak of the disease. Though the disease 
has not reached the populous centers of northern, eastern, or southern Africa 
and India, yet the possibilities of modern transportation are constant sources 
of danger. Unless reduction of the yellow-fever mosquito is brought about, 
the appearance of the disease in any of these populous regions might mean a 
disaster of serious proportions, despite the use of the vaccine (as witness the 
outbreak in 1940 in the Anglo-Egyptian Sudan). Furthermore, new endemic 
centers would be established and the continued spread of the disease would 
be assured. In recent years (1933) the discovery of jungle yellow fever in 
South America has added a new problem to yellow-fever control. This should 
emphasize more strongly the need for urban control of Aedes aegypti and 
the more extensive use of the vaccine in suspected areas. 

Though dengue is a disease of low mortality, yet the lowered vitality of 
its victims and the rapidity of its spread warrant special consideration. As 
Aedes aegypti is the only known transmitter in America, we must assume 
that it breeds in vast numbers in many southern states, as witness some 
500,000 to 600,000 cases of dengue in Texas in 1922. The control of the mos- 
quito is apparently not very effective in the United States. Here again the 
elimination of the breeding places of the yellow-fever mosquito should be a 
major consideration in every city and village where it occurs. 

Malaria, unlike yellow fever and dengue, is primarily a disease of rural 
districts, small cities, and villages. The anopheline transmitters do not breed 
to any extent in artificial water containers but are primarily restricted to more 
or less permanent bodies of protected fresh water, slow-running streams, 
marshes, swamps, and, with certain species, to brackish water along coastal 
areas. Fortunately all anophelines are not "good" or "dangerous" transmitters 
of malaria. In recent years consistent efforts have been made to determine 
these "dangerous" transmitters, discover their specific breeding grounds, 
their bionomics, etc., and then concentrate all efforts, at first, to the control of 
such species. The results of such directed endeavors have been very gratifying 
in certain countries as the Federated Malay States, the Canal Zone, Palestine, 
etc. Whether such principles can always be applied remains for the future 
to decide. The reduction and control of anopheline vectors of malaria are 
highly specialized procedures. Such work should be guided by well-trained 



398 MEDICAL ENTOMOLOGY 

malariologists and entomologists, and the procedure to be followed must be 
based on a sound knowledge of the bionomics of anopheline vectors in any 
particular region (witness the problem of A. gambiae in Brazil). 

PLAN OF ORGANIZATION 

In order to plan and carry out mosquito control, a well-organized unit is 
essential. Such an organized division should be in close association with or 
directly under the officer in charge of public health work. This work may be 
done under local regulations or, where several communities unite, under a 
specific state or provincial law 3 empowering townships, districts, or counties 
to organize mosquito abatement districts. In any such organized district the 
work of mosquito control should be under a responsible, well-trained en- 
tomologist, or one familiar with the problems of mosquito biology. The suc- 
cess or failure will largely depend on his ability and freedom to plan and 
carry out effective measures. The budget for the proposed work should be 
independent and appropriated specifically for mosquito-control work. The 
officer in charge should be granted wide discretionary powers, and he should 
have authority to carry out well-planned schemes that may involve either 
private or public rights. 

Such an officer should have authority to secure the co-operation of all 
public and private planning commissions, and all private or public bodies 
engaged in any operations that involve or may involve the formation of ponds, 
reservoirs, or impounded water, or that deal with building, street, road, and 
real estate developments, drainage schemes, etc. Only in this way will the 
officer have an opportunity to inspect all plans that might compel him to 
modify his scheme of mosquito control. The organized unit should include 
trained inspectors and laborers. The numbers and their equipment will be 
dependent on the extent of the abatement district and the difficulties involved. 
Furthermore, the officer should have authority to engage sanitary engineers 
and other experts when highly technical plans have to be prepared and car- 
ried out. In this way, one person will be held responsible and his success 
or failure can easily be judged by the mosquito density in his district. 

Another important duty will be to aid the health authorities, public works 
departments, etc., in drawing up careful sanitary, drainage, and water storage 
regulations involving all conditions that may increase or decrease mosquito 
breeding. The expense of such an organization will depend on many factors. 
There is one consideration, however, that should outweigh the cost: any 

3 Such laws are in effect in New Jersey, California, Illinois, and probably many other 
places. The New Jersey law seems the most far-reaching and adequate in our country. 



PROBLEM OF MOSQUITO CONTROL 399 

work done should be well done, a long-time plan of operations should be 
obtained, and a continuing policy should be assured. Furthermore, the cost 
of the improvements to public and private property may largely be charged 
to such properties and the general increase in taxable values should far ex- 
ceed the costs. 

REFERENCES 4 

*Aitken, T. H. G. A study of winter DDT house spraying and its concomitant 

cflects on anophelines and malaria in an endemic area. Jl. Nat. Mai. Soc., 5: 

168-187, 1946. 
American Mosquito Control Association. The use of aircraft in the control of 

mosquitoes. Amcr. Mosq. Con. Assoc., Bull. I, 1948. 
Clapp, J. M., Fay, R. W., and Simmons, S. W. The comparative residual toxicity 

of DDT to Anopheles quadrimaculatus when applied on different surfaces. U.S. 

Pub. Illth. Rcpts., 62: 158-170, 1947. 

Connor, M. E. Fish as mosquito destroyers. Nat. Hist., 21: 279-281, 1921. 
**Covcll, G. Malaria control by anti-mosquito measures. London, 1931. 
Crawford, }. A. Mosquito reduction and malaria prevention. London, 1926. 
*Hall, T. F., Pciifound, W. T., and Hess, A. D. Water level relationships of 

plants in the Tennessee Valley with particular reference to malaria control. Jl. 

Tenn. Acad. Sci., 21: 18-59, 1946. 

Hardenhurg, W. E. Mosquito eradication. New York, 1922. 
*Hcrms, W. R., and Gray, H. F. Mosquito control. New York, 1944. 
Hewitt, R., and Kotcher, E. Observations on household anophelism in a selected 

group of mosquito-proofed and non-mosquito-proofed homes. U.S. Pub. Hlth. 

Repts., 56: 1055-1061, 1941. 

Hildebrand, S. F. A study of the top minnow, Gambusia holbroofy, in its rela- 
tion to mosquito control. U.S. Pub. Hlth. Serv., Bull. 153, 1925. 
*Hinman, E. H. A study of the food of mosquito larvae. Amer. Jl. Hyg., 12: 

238-270, 1930. 
*Kligler, I. }. The epidemiology and control of malaria in Palestine. Chicago, 

1930. 
*Knipling, E. F., ct aL Evaluation ot: selected insecticides and drugs as chemo- 

therapeutic agents against external bloodsucking parasites. Jl. Parasit., 34: 55-70, 

1948. 
Kruse, C. W., and Metcalf, R. L. An analysis of the design and performance of 

airplane exhaust generators for the production of DDT aerosols for the control 

of Anopheles quadrimaculatus. U.S. Pub. Hlth. Repts., 61: 1171-1184, 1946. 

4 The literature on mosquito control is very great. Fortunately several extensive ac- 
counts have recently been published and most of these contain bibliographies. Only a 
few references can be included here and the reader is referred to them for further in- 
formation. 



400 MEDICAL ENTOMOLOGY 

*LePrince, J. A., and Orenstein, A. }. Mosquito control in Panama. New York, 
1916. 

*Matheson, R. The utilization of aquatic plants as aids in mosquito control. 
Amer. Natur., 64: 56-86, 1930. 

New Jersey Mosquito Extermination Association. Proceedings . . . Vols. I-. 
New Brunswick, N.J., 1914-. Valuable papers each year on mosquito prob- 
lems. 

Penfound, W. T. The relation of plants to malaria control with special reference 
to impounded waters. U.S. Pub. Hlth. Repts., 57: 261-268, 1942. 

* , et al. The spring phenology of plants in and around the reservoirs in north 

Alabama with particular reference to malaria control. Ecology, 26: 332-352, 
1945. 

Senior-White, R. Progress towards the realization of biological control of mos- 
quito breeding. Trans. Cong. Far East Assoc. Trop. Med. (yth Cong.), 2: 718- 
722, 1929. 

Soper, F. L., and Wilson, D. B. Anopheles gambiae in Brazil. New York, 1943. 

, et al. The organization of permanent nation-wide anti-Aedes aegypti meas- 
ures in Brazil. New York, 1943. 

* , et al. Reduction of anopheles density by the pre-season spraying of build- 
ing interiors with DDT in kerosene, at Castel Volturno, Italy in 1944-1945 and 
in the Tiber Delta in 1945. Amer. Jl. Trop. Med., 27: 177-200, 1947. 

Speer, A. }. Compendium of the parasites of mosquitoes. U.S. Pub. Hlth. Serv., 
Hyg. Lab., Bull. 146, 1927. 

Stromquist, W. G. Engineering aspects of mosquito control. Civil Eng., 14: 

43i-434> J 944- 

U.S. Public Health Service and the Tennessee Valley Authority. Malaria control 
on impounded waters. Washington, 1947. (A most valuable work by many 
authorities on impounded water and the problems of malaria control by anti- 
mosquito measures.) 

Upholt, W. M., et al. The experimental use of DDT in the control of the yellow 
fever mosquito, Aedcs aegypti. U.S. Pub. Hlth. Repts., Suppl., 186: 90-96, 
1945. 

Watson, M. The prevention of malaria. London, 1921. 

. Twenty-five years of malaria control in the Malay Peninsula, 1901-1926. Jl. 

Trop. Med. Hyg., 32: 337-340, 1929. 

Watson, R. B., and Rice, M. E. Further observations on mosquito-proofing for 
malaria control. Amer. Jl. Hyg., 34: 150-159, 1941. 



CHAPTER XIII 



Other Bloodsucking 
Nemocerous Flies: 

Simuliidae and 
Ceratopogonidae or Heleidae 



IN ADDITION to the mosquitoes (Culicidae) and the moth flies (Psy- 
chodidae) two other families of Nemocera contain bloodsucking species. 
These flies are all very small, some of them extremely minute, but many of 
them are vicious biters and extremely annoying to man and animals. Re- 
cently certain species have been proved or incriminated as transmitters of 
important diseases. As these flies are world-wide in distribution, often ex- 
tremely abundant in individuals, attack man and animals with terrible 
severity, and are now known to transmit certain diseases, the study of them 
has attracted considerable attention in recent years. Owing to their minute 
size and the difficulties involved in the study of their life histories, not as 
much progress has been attained as could be desired. 

FAMILY SIMULIIDAE 

The Black Flies, the Buffalo Gnats 

The Simuliidae may be recognized by their small size (i to 6 millimeters 
in length), stout bodies, short legs, and characteristic "humped" appearance 
due to an arching of the thorax (Fig. 145). The wings (Fig. 145) are broad 
with the anterior veins well developed, the others indistinct. The antennae 
are nine, ten, or eleven jointed and usually not as long as the head; the seg- 
ments are short, closely pressed together, and bear numerous short hairs. In 
the males the eyes are contiguous (holoptic), while in the females the eyes 



402 



MEDICAL ENTOMOLOGY 



are rather widely separated (dichoptic). The mouth parts are formed for 
piercing and sucking. Only the females are known to take blood. 

The family includes at present a rather large number of species. Williston 
(1908) reported only about 75 species in all the world, but Bequaert (1931) 




Fig. 145. The black fly, Simulium arcticum Malloch. Male above, female 
below. Veins are labeled according to the Comstock system. (From Cameron.) 

records some 330 species, distributed as follows: 125 for the Palearctic region, 
53 for the Nearctic, 80 for the Neotropical, 24 for the Ethiopian, 26 for the 
Oriental, and 24 for the Australasian. Dyar and Shannon (1927) report 47 
species for North America and Greenland, and Bequaert (1926) indicates 
70 species for South and Central Americas. Smart (1945) lists 623 world 



OTHER BLOODSUCKING NEMOCEROUS FLIES 403 

species; Vargus (1946) adds 23 species to this list. The family is world- wide 
in distribution, extending from the tropics to the Arctic Circle and to eleva- 
tions of at least 9000 feet. 

STRUCTURE OF THE MOUTH PARTS: The mouth parts constitute 
a short proboscis composed of the following parts: The labrum. This is an 
elongated unpaired structure (in cross section like a three-sided pyramid) 




Fig. 146 (If ft). Lateral view of the mouth parts of a black fly (Eusimulium lascivum} 
to show the relationship of the various parts and their muscles. Comp Ibr-ep, compressor 
muscles of the labrum; Dil ant oes, dilator muscle of the anterior esophagcal pump; 
Dil ph, dilator muscle of the pharyngeal pump; Dil p oes, dilator muscle of the posterior 
csophageal pump; Dil sal pmp, dilator muscle of salivary pump; Fr cl, frontoclypeus; 
Hyp, hypopharynx; Lbr-ep, labrum; Lev Ibr ep, Icvator muscle of labrum; Oes pmp, 
esophageal pump; Ph pmp, pharyngeal pump; Ret ph, retractor of the pharyngeal pump; 
Sal ch, salivary channel; Sal d, salivary duct; Sal g, salivary gland; Sal pmp, salivary 
pump; Tens fr cl, tensor of the frontal clypcus. (After Krafchick.) 

Fig. 747 (right). Mouth parts of Prosimulium hirtipes. Left: Mandible. Right: Left max- 
illa, dorsal view. C, cardo; D, depression in mandible with elevation on opposite side; G, 
galca; P, palpus; S, stipes; SP, sensory organ. (Maxilla drawn at twice the scale of man- 
dible.) 

movably attached to the membrane suspended from the frontoclypeus. It is 
continued directly forward from the head as a strong convex plate strength- 
ened medially and laterally by sclerotizecl bars that meet at the distal ex- 
tremity. The base of each labral bar is more or less Y-shaped, the arms of the 
Y forming the bases of the lateral walls. These arms meet extensions from 
the head and the lower anterior walls of the pharyngeal pump. These points 
of contact form the fulcra for the levation and depression of the labrum. The 
arrangement of these parts and their muscles are shown in Fig. 146. The tip 



4 o4 MEDICAL ENTOMOLOGY 

of the labrum is provided with denticles on each side of the median line. 
The mandibles (Fig. 147) consist of a pair of broad spatulate structures, 
sharply pointed distally and provided with numerous small recurved teeth 
along the apical margin. Each mandible has, near its middle, a small area with 
a depression on one side and an elevation opposite. In the position of rest the 
mandibles are closed scissorlike and lie between the labrum and hypopharynx. 
They are locked together by means of the device just mentioned, the elevation 
on one fitting into the depression of the other as first observed by Jobling (1928) 
for Culicoides. The maxillae (Fig. 147) are paired structures, arising just be- 
low the mandibles. Each maxilla has the usual parts: cardo, stipes (these 
two usually united), galea, and palpus. The galea has a curved, basal, sclero- 
tized arm, which terminates in a vicious-looking, swordlike cutting structure 
(Fig. 147). The margins of the blade are recurved ventrally and bear rctrorse 
teeth. The palpus consists of four segments (the basal one subdivided) ; the 
second segment has a deep pit in which is probably located a sensory organ. 
The hypopharynx is an unpaired organ lying below, and in close union at 
the base with, the labrum. It arises from the floor of the pharynx, with which 
it is joined by a hingelike arrangement. It is deeply concave on its dorsal side 
and its sclerotized margins receive, in V-like notches, the extensions of the 
lateral bars of the labrum. The salivary pump is attached near the base of 
the hypopharynx, and the salivary duct perforates the base of the hypopharynx 
and extends along its middle to near the apex. Back of the pharynx lies the 
pharyngeal pump. The labium consists of two lobes, each of which is con- 
cave anteriorly so that the mouth parts are concealed within when at rest. 
Each lobe is composed of three segments. The proximal parts are fused along 
the posterior mid-line while the other segments are free. The fused basal 
segments probably represent the theca and the free segments the labellae. 

The action of the mouth parts in obtaining blood has not been observed 
or carefully described. In all probability they function as in Culicoides as de- 
scribed by Jobling (1928). He says, in describing their action, 

It was noted that the labrum-epipharynx, the hypopharynx, and the mandibles 
interposed between these two parts, compose together a piercing stylet which per- 
forms forward and backward movements during biting. When these mouthparts 
have penetrated a little more than half their length into the skin, the protraction 
and retraction cease. During the sucking of blood the mandibles are not withdrawn 
to the sides, but by the structure of their middle parts they are maintained 
between the labrum-epipharynx and hypopharynx. Thus the food canal is formed 
by them and the labrum-epipharynx as has already been indicated by Leon (1924), 



OTHER BLOODSUCKING NEMOCEROUS FLIES 405 

The labium functions as a guide, holding the mouth parts in position while 
making the puncture. The action of the maxillae could not be observed by 
Jobling, but he thinks the galea moves forward and backward, thus having 
a tearing action. 

BIOLOGY: The larval stage of all known species is passed in running 
water. The larvae are found in swift currents, at the edge of waterfalls, on 
rocks where the water sweeps by (Fig. 148), in shallow mountain streams, 









;.:/.: ..... :::.. 



Fig. 148. Note the large stone sticking above the swift-running water. Near 
the water's edge and on the rock are large numbers of males of Eusimulium 
muttatttm waiting for the emergence of the females. Below are large masses of 
larvae and pupae'of this species. 

in roadside ditches, and in similar situations. They attach themselves by means 
of an anal disc (see below) and retain their position even in very swift water. 
They are usually found in the shallower parts of the streams, especially 
where the water breaks over some obstruction, or attached to floating grasses 
or other pendulous plants. 

The eggs are laid at the level of the water, or just below, on any convenient 
surface as bare rocks, debris, or other smooth objects (Simulium pictipes) ; on 
blades of grass trailing at the surface of the water (S. vittatum, S. venustum, 
S. bracteatum) ; or under the water to a depth of a few inches to a foot. 
Bradley (1935) states that Cnephia pecuarum drops its eggs directly in the 



4 o6 MEDICAL ENTOMOLOGY 

flowing water; the eggs are heavier than the water and they settle to the 
bottom. The total number of eggs a single female may lay is not known, 
though Pomeroy (1916) records 349 eggs laid by one female, under experi- 
mental conditions, in twelve minutes. Other records indicate a female may 
lay as many as 500 or more eggs at one oviposition. According to most 
observations, oviposition takes place during the evening hours from four to 
about eight o'clock. The eggs are minute, about 0.25 mm. in length and some- 
what triangular in shape. They hatch in from 4 to 12 days or more, depending 
largely on temperature and aquatic conditions, or they may remain dormant 
for a long time. 

The larvae (Fig. 149) of the Simuliidae can usually be recognized from 
their habitats. The more common, easily observed characters are the form of 
the body generally subcylindrical, usually enlarged at each end, and at- 
tenuated in the middle; the possession of two large fan-shaped organs on the 
head; a short median leg armed with hooks on the ventral surface of the 
segment back of the head; a disc provided with rows of hooks arranged in 
circles on the posterior end of the body; and the presence of characteristic 
anal gills (blood gills). The larval stages of comparatively few species have 
been fully described. Edwards (1920) has summarized his work on the 
British species; Pomeroy (1916) has carefully described five American 
species; Friedcricks (1920) many of the more common species of Germany; 
Puri (19^2-19^) the Indian species; Gibbins (1933-1937) aac ^ Bequaert 
(1938) certain African species; Bequaert, HofTman, and Vargas a number 
of species from Central America and Mexico; and Twinn (1936) many 
Canadian species. 

The larva, on escaping from the egg, attaches to the nearest object by 
means of the thoracic proleg. The body is then moved about till the sucker- 
like anal disc can be brought into contact and more or less permanent attach- 
ment follows. According to Wu (1931), the anal disc is not a true sucker 
but attachment is brought about by glutinous material placed on the disc 
by the mouth. The larvae are capable of movement, looping from place to 
place by means of the proleg and anal disc. According to Puri (1925), this is 
accomplished as follows: the larva places some saliva on a selected spot and 
fixes the proleg to this spot; it then places saliva in front of the previous spot 
and, withdrawing the anal disc, attaches it to the new saliva. In this manner 
the larva can move slowly about. It also spins a silken thread from the salivary 
glands and can use this as a means of dropping down stream and then crawl 
back on the thread to the place of attachment. 

The larva undergoes six molts, pupation occurring at the last molt. The 



OTHER BLOODSUCKING NEMOCEROUS FLIES 



407 



duration of the larval period varies widely. Puri records four to six weeks 
(S. aureum and S. erythrocephalum) during the summer; Pomeroy notes 
full larval development in South Carolina in 17 days (S. venustum, S. brae- 





Fig. 149. (/) Dorsal view of larva of Simulium arcticum. (2) Pupa in its pupal case. 
(^) Pupa removed from pupal case. (4) Pupa, ventral view. (5) Lateral view of larva 
of Simulium pictipes. (6) Pupa in its case, lateral view. (7) Lateral view of pupa. 
F, mouth fans; G, blood gills; P, median prothoracic leg; S, posterior sucker; Tg, tracheal 
gills. (/ to 4 from Cameron; 5 to 7 from Johannsen.) 

teatum, S. vittatum, and S. pictipes)', Cameron (1922) states that S. arcticum 
(simile) requires three to four weeks in western Canada; Wu (1931) records 
13 to 17 days for S. vittatum in Michigan. 
Pupation takes place in the larval habitat. The larva spins a silken cocoon 



408 MEDICAL ENTOMOLOGY 

(Fig. 149) within which the pupal period is passed. The pupal stage varies 
from two to seven days, or longer in cooler weather. The adults, on emer- 
gence, rise to the surface of the water and take to wing. 

The number of annual generations varies greatly in different parts of the 
world. Pomeroy thinks that there are five or six generations in South Carolina; 
Cameron records four generations for S. arcticum (simile) ; Edwards thinks 
there is but one generation of S. venustum and S. reptans, two generations of 
S. latipes, three of S. equinum and S. ornatum, and four generations of S. 
argyreatum in England. Smart (1934) states there are four or five annual 
generations of S. pictipes in central New York; Prosimuliitm magnum has 
only one generation in the same area; P. hirtipes has frequently two genera- 
tions in the Adirondack region of New York state and this is also true for 
Simulium venustum; Twinn (1936) records two or three generations of S. 
vittatum Zett. in Ontario and Quebec. Bradley (1935) records only a single 
generation a year for Cnephia pecuarurn. 

The adults are vigorous fliers and have been recorded four or more miles 
from their breeding grounds. Cameron (1922) records a 1 2-mile flight for 
S. arcticum. It is believed that their migratory habits are induced by their 
desire for blood, blood being the principal food of the adults (females). Most, 
if not all, the species are bloodsucking in habit (S. aureum is not known to 
take blood; S. pictipes is also thought to be an exception but it has been re- 
corded as feeding on mules). Certain species seem to prefer the blood of 
particular animals though other species are more catholic in their tastes. 
Thus Pomeroy states that S. venustum seldom attacks man or cattle but is a 
severe pest of horses and mules, feeding within the ears. Dyar and Shannon 
(1927) report the same species as very annoying to man, and this agrees with 
the writer's experience. Bequaert (1938) summarizes the data on the feeding 
habits of black flies. Some feed largely on birds as S. bracteatum Coq. 
( aureum Fries), S. venustum Say (important pest of ducks), S. atratum 
de Meij. (on birds in Java), S. virgatum Coq., and S. mexicunum Bellardi 
(on horses but not man in Guatemala); only 5 of the 57 species of the 
Ethiopian region attack man (S. damnosum Theo., S. naevei Roub., S. adersi 
Pom., S. willmani Roub., and S. griseicole Beck.). In addition we may add S. 
venustum Say and S. hirtipes Fries as severe pests of man in their ranges. 
Twinn (1936) reports S. vittatum Zett. as feeding on horses; S. arcticum Mai. 
is a severe pest of cattle, horses, and sheep; and in Mexico S. metallicum Bel- 
lardi, S. ochraceum Walk, and S. callidum D. & S. are known to bite man. 
Other species are known to be very destructive to animals including man, as 
Cnephia pecuarum (Riley) and S. columbaschensis Fabr. 



OTHER BLOODSUCKING NEMOCEROUS FLIES 409 

CLASSIFICATION: The family Simuliidae has been rudely treated by 
the taxonomists. It has been divided into six or more subfamilies with nu- 
merous genera and subgenera (Enderlein, 1921). Edwards (1931), however, 
recognized but a single genus, Simulium, and seven subgenera. Vargas (1945) 
recognized but one genus, Simulium, for the New World species. Smart 

(1945) recognized two subfamilies and six genera from the world. Vargas 

(1946) adopts the classification by Smart but in addition adopts nine sub- 
genera in the genus Simulium (restricted). The following key (adapted from 
Smart) will serve to separate the genera : 

T. R, of the radius joining the costa about the middle of the front margin 

of the wing; radial sector (Rs) forked, (i sp., California) 

Parasimulium 

R t of the radius joining the costa well beyond the middle of the front 
wing (Fig. 145) ; radial sector forked or not 2 

2. Radial sector (Rs) forked; pedisulcus and calcipala lacking. (28 spp.) 

Prosimulium 

Radial sector (Rs) not forked (Fig. 145); pedisulcus and calcipala (Fig. 
150) may be present or absent 3 

3. Vein Cu 2 straight; anal vein straight; pedisulcus absent; calcipala well 

developed. (Neotropical; 13 spp.) Gigantodax 

Vein Clio sinuous (Fig. 145) ; anal vein sinuous 4 

4. Antennae with 10 segments or less (mainly Australian and Andean re- 

gion of S. America) Austrosimulium 

Antennae with n segments; rarely 10 5 

5. Pedisulcus absent or very indistinct; calcipala minute or absent; basal 

section of radius lacks macrotrochia above; distal section of radial sector 
with a single row of macrotrichia above. (World-wide; 36 spp.) .... 

Cnephia 

Pedisulcus present; calcipala present (Fig. 150); basal section of radius 
and distal section of radial sector with or without macrotrichia. (World- 
wide; over 500 spp.) Simulium 

It is not feasible to give keys to species as many characters are based on the 
male or female genitalia. Keys will be found in some of the references cited 
and these are indicated. 

RELATION TO DISEASE 

The black flies or buffalo gnats affect man and animals in at least two ways, 
by their bites and as intermediate hosts of parasites. 



4io MEDICAL ENTOMOLOGY 

BITES : The bites of black flies are extremely annoying. The flies commonly 
appear in swarms and attack with great avidity. Various species have been 
recorded from the tropics to the polar circles as inflicting severe damage to 
stock and causing a peculiar fever in man. Probably the most famous species 
is the Golubatz fly (S. columbaschensis Fabr.), which frequently occurs in 
countless numbers in parts of Romania, Yugoslavia, and Hungary. Ciurea 
and Dinuflescu (1924) paint a gloomy picture of an invasion of this fly in 
certain parts of Romania during the season of 1923. Domestic animals suffered 
severely and the authors record the death of 16,474; l ar g e numbers of wild 
animals, as foxes, deer, and hares, were also killed. Though man was also 
severely attacked and suffered from their bites, no deaths are on record. 
Riley (1887) gives an extended account of outbreaks of Cnephia pecuarum, 
the buffalo or turkey gnat, in the lower Mississippi Valley. Mules, horses, 
cattle, sheep, sitting turkeys and hens, hogs, dogs, and cats suffered in the 
order named. Large numbers of these animals were killed, especially mules, 
horses, turkeys, hens, and hogs. Cattle also succumbed if weakened from 
poor food and exposure. There also appear reports of deaths of human beings 
but most of them seem doubtful. Webster (1904) gives a striking account 
of the plagues of this fly in the same region. Bradley (1935) reports heavy 
losses of mules in Mississippi and eastern Arkansas in 1927, 1931, and 1934. 
A total of over 1600 were killed during these years. Rempel and Arnason 
(1947) describe the mass attack of Simttliitm arcticum Mai. on horses, cattle, 
and sheep. The animals began dying within 6 to 24 hours after the attack. 
If cold weather intervened, the flies disappeared, and this happened in some 
of the worst outbreaks. In all, over 800 cattle, horses, and sheep were killed 
during the years 1944, 1945? and 1946. Various travelers and explorers give 
weird accounts of the abundance of black flies and the suffering caused by 
their bites. Wilhelmi (1920) presents an excellent summary of black-fly 
plagues (die Kriebelmticl^enplagc). 

Stokes (1914) carefully investigated the effects of the bites of Simulium 
vennstum. The typical bite in a susceptible individual appears to run the 
following course: bite painless, followed by hemorrhagic spots or red patches; 
a papular lesion develops in 3 to 24 hours, and later a vesicular lesion which 
may last for a few days to several weeks. The lesions from several nearby 
bites may become confluent presenting a large vesicopapular lesion with 
considerable exudate followed by extensive edema, and the formation of 
oozing and crusted plaques. Pruritus (intense itching) begins shortly after 
the bites and may become diffuse with considerable heat and burning sensa- 
tion; the pruritus may return periodically even after the lesions have ap- 



OTHER BLOODSUCKING NEMOCEROUS FLIES 411 

patently healed. Frequently the intense itching, followed by scratching, may 
cause secondary infection with more serious results. As the flies frequently 
attack back of the ears, over the eyes, cheeks, and neck, inflammation and 
edema at these sites may be marked. In addition to the lesions, pruritus, etc., 
produced by the bites, most people suffer from swelling of the lymphatic 
glands (lymphangitis), which become tender and painful on pressure. These 
swellings usually subside without further trouble if the patient is not sub- 
jected to further black-fly attacks. Stokes records no constitutional effects 
from the bites though such have been noted by other workers. 

There appears to be considerable immunity to the bites of black flies. Many 
persons reared in black-fly areas seem to acquire a certain immunity. The 
writer has suffered agonies from their bites, while native companions re- 
mained unattractive to the flies and unbitten. I have seen fishermen come 
from the woods with their faces streaming with blood due to black-fly bites 
but they suffered no apparent harm; others show distinct feverishncss, irrita- 
tion, and intestinal disturbances; in one case a lineman was brought in almost 
unconscious from continued exposure but he recovered in a few days. 

The presence of these flies renders many attractive areas almost unhabitable 
during certain seasons of the year. Though attempts have been made to 
immunize man against their bites, no great success has been achieved. The 
activating agent in the causation of the vesicular papules, pruritus, etc., is 
believed to be in the secretions of the salivary glands but what it is remains 
as yet unknown. 

DISEASE: Though black flies have been accused of transmitting diseases, 
it is only within the past few years that definite experimental work has proved 
them to be intermediate hosts of human parasites. 

Onchocerciasis is an infection due to species of Onchocerca (family Filari- 
idae of the Nemathelminthes). Onchocerca volvulus Leuck. causes subcuta- 
neous tumors that vary from small, smooth nodules to swellings as large 
as a walnut (Fig. 151). In many cases no nodular swellings may occur, though 
the microfilariae can be recovered from the skin, the subcutaneous lymph 
channels, and the peripheral blood. This parasite was first found in a native 
of the Gold Coast, Africa, in 1893. Since then it has been found widely dis- 
tributed along the west coast of Africa and from Sierra Leone to the Congo 
basin, east to southern Sudan, Uganda, Nyasaland, Kenya, and other parts 
of Africa. Blacklock (1926) reports that 40 to 50 per cent of the natives ex- 
amined in Sierra Leone had the microfilariae of 0. volvulus in their skins. 
In the same year he elucidated the further development of this worm in its 
insect vector. He discovered that a black fly, Eusimulium damnosum Theo., 



4 i2 MEDICAL ENTOMOLOGY 

ingests these microfilariae; the ingested microfilariae show great activity in 
the gut of the fly and on the second day after feeding they are found in the 
posterior thoracic muscles; here development proceeds and molting ap- 
parently occurs. At the end of a minimum of six or seven days mature 
larvae are found in the labium of the proboscis and are ready to infect new 
hosts when the fly bites. Only man has been found naturally infected with 




Fig. 150 (left). Hind leg of Simulium vittatum. Cal, calcipala; F, femur; Peel, pedisul- 
cus; Tb, tibia. 

Fig. 757 (right). Onchocerciasis. Note nodules on elbow and hip. (After Blacklock, 
Annals of Tropical Medicine and Parasitology.) 

O. volvulus. Though no transmission experiments by means of experimen- 
tally infected flies have been attempted on man, it is believed that Simulium 
damnosum is the vector. Experiments with monkeys were negative. Though 
S. damnosum is widely distributed in tropical Africa, its early stages and 
breeding habits are apparently unknown. 

Onchocerca caecutiens Brumpt was first found by Robles in 1915 in nodules 
on the scalp of about 95 per cent of the population of the Pacific slope of 
Guatemala at elevations between 600 and 2000 meters. The infection, in a 
certain proportion of cases, shows no clinical symptoms, but many have 



OTHER BLOODSUCKING NEMOCEROUS FLIES 413 

painful erysipelaslike swellings; hence it is called "coastal erysipelas." Recent 
workers seem to consider O. caecutiens identical with O. volvulus. Hoffman 
(1930) reports that all the people in certain parts of Chiapas, Mexico, have 
the microfilariae in the lymph and 86 per cent show nodular swellings. The 
nodular swellings occur, not only on the head, but on the iliac crests, ribs, 
shoulder blades, and other parts of the body. Ochoterena (1930) demonstrated 
the microfilariae in the excised eye of a blind man, the "embryos congregating 
in the outer third, in the corneal epithelium." Strong (1931) confirmed these 
results and states that the continued passage of these microfilariae through 
the lymphatics of the eye for long periods may cause conjunctivitis, keratitis, 
and iritis. It would thus seem that this parasite in Africa, Central America, 
and Mexico may be the causative agent of certain types of blindness. 

Hoffman (1930) first traced the development of this microfilaria in a black 
fly, Simulium callidum D. & S. ( mooscri). He showed that the micro- 
filariae, after being ingested by the black fly, pass from the intestine to the 
thoracic muscles where further development takes place. The develop- 
mental period in the fly is six or more days, and the infective stage passes to 
the mouth parts where the microfilariae are ready to infect new individuals 
when the fly bites. Hoffman, Strong, et al. and others have amply demon- 
strated complete development of this parasite in the following black flies in 
Mexico: Simulium metallicum Bellardi ( avidttm HofTman), S. ochraceum 
Walk., and S. callidum D. & S. ( ~ mooseri Dampf). 

In addition to the human diseases transmitted by black flies, O'Roke has 
shown that Simulium venustum Say transmits a malarialike disease of ducks 
caused by a protozoan, Leucocytozoon anatis Wickware. This disease is said 
to be very deadly to young ducklings. Johnson (1942) reports a Leucocytozoon 
of turkeys transmitted by S. nigroparvum Twinn. Steward (1937) has demon- 
strated the life cycle of Onchocerca gutterosa Neum. (a parasite of cattle) in 
the black fly, Simulium ornatum Meig. in England. 

PROTECTION FROM BITES: Though certain persons claim immunity 
to black-fly bites, the effect on the average person is usually severe, even 
causing clinical symptoms of disease. Recently the United States Bureau of 
Entomology and other agencies during World War II have developed ex- 
cellent repellents for mosquitoes, and some of these are effective against 
black flies. These are dimethyl phthalate and indalone. Everready or 612, 
developed at Rutgers University, is also an excellent repellent. Dimethyl 
phthalate and 612 are effective for about a maximum of four to six hours. 
Apply these repellents to all exposed parts but avoid getting them into the 



4 T 4 MEDICAL ENTOMOLOGY 

eyes; they may also be applied to stockings or other clothing through which 
the flies may bite. These repellents are pleasant, noninjurious to the skin, 
and can be applied as often as necessary. 

CONTROL OF BLACK FLIES : The control of black flies is very difficult. 
As their breeding grounds are mainly swift or slow-flowing streams of all 
sizes, it does not seem possible to destroy the larvae except by the use of 
chemicals that may kill nearly all animal and plant life. The amount of such 
chemicals needed would be very great in some rivers where these flies often 
breed in vast numbers. In the smaller streams, however, breeding can be 
reduced by the removal of debris, such as logs, branches, stumps, stones, 
floating weeds or grasses, or other obstructions. The cost is usually excessive. 
Attempts have been made to reduce breeding by the application of DDT 
either as an oil emulsion or water suspension. The results are not very en- 
couraging as the amount of DDT required kills so much of the other valuable 
animal life. It may be possible to devise methods and ascertain amounts that 
are effective against black-fly larvae but not injurious to other life in the 
streams. 1 

The adults, when abundant, may be killed by DDT as aerosols, mist sprays, 
etc., applied by airplanes, helicopters, or special ground equipment. Such 
methods have been applied extensively against hordes of mosquitoes and have 
proved satisfactory to those who pay for the expenditures. 

FAMILY CERATOPOGONIDAE (Heleidae) 
The Punkies, No-scc-ums 

The Ceratopogonidac contains a small number of known species, usually 
referred to as "punkics." This family may be distinguished by the long an- 
tenna (13 to 15 segments) ; the short proboscis (Fig. 154) ; and the membrane 
of the wings which bears micro- and macrotrichia and is commonly orna- 
mented, in some genera, with dark spots and pale areas (Fig. 153). The 
family contains a considerable number of genera but only about four have 
species that are bloodsucking in habit. These are Leptoconops, Lasiohelca, 
Holoconops, and Culicoides. The most important genus is undoubtedly 
Culicoides. 



1 Recent reports indicate that black-fly larvae can be destroyed, even in large streams, 
by airplane spraying some distance above their breeding grounds. How effective these 
measures are and the correct amounts of DDT to use have not been adequately determined. 
The destruction of other aquatic life in these streams is a problem that has not been 
solved satisfactorily. 



OTHER BLOODSUCKING NEMOCEROUS FLIES 415 

KEY TO THE GENERA 2 

(Adults bite man or animals) 

1. Racliomedial cross vein absent; antennae of females with 13 to 14 seg- 

ments (including pedicel and minute scape) 2 

Radiomedial cross vein present; media with two branches; antennae of 
females with 15 segments (including pedicel and minute scape) .... 3 

2. Antenna of female with 14 segments Leptoconops 

Antenna of female with 13 segments Holoconops 

3. Empodium well developed, nearly as long as the claws. First radial cell 

small and narrow; second cell long and narrow. (Severe bloodsuckers; 

S. American) Lasiohelea 

Empodium small or vestigial; claws small and simple; two radial cells 
usually present and second branch of radius ends beyond middle of 
wing; wings usually spotted. (A large genus) Cttlicoides 

THE GENUS CULICOIDES 

The flies belonging to this genus are all bloodsucking and arc usually 
known as "punkics." (The term "sand flies" is frequently used but this should 
be restricted to the bloodsucking species of Psychoclidae.) They are extremely 
annoying and on account of their small size (only i to nearly 3 mm. in length) 
can easily pass through the openings of the ordinary mosquito screens. In 
some parts of the tropics and subtropics they are so abundant as to interfere 
seriously with the development of certain regions. Their mouth parts (Fig. 
152) are admirably adapted for taking blood and closely resemble, in structure, 
the mouth parts of the Simuliidae. The males are not known to take blood. 

LIFE HISTORY: Oviposition has apparently been observed in only one 
species, C. tyefferi Patton. This species lays its eggs in a mass in the vicinity 
of water, on some algae or green plant growth. Other species undoubtedly 
lay their eggs in a similar manner. The larvae arc found only in water or in 
water-saturated sand or soil, both brackish and fresh, where there is decaying 
vegetation. They like water holes in stumps, tree holes, and manure heaps 
and water-holding plants; a few may be found in slime-covered bark of trees 
and under bark and rotting vegetation. The larvae (Fig. 154) are minute, 

2 The number of genera in this family varies widely depending on the author; 
Johannsen (1943) recognizes 45 genera in the Americas. Those indicated above are the 
only genera in which the species are bloodsucking in habit. For keys to genera and 
species, consult the bibliography. 



416 MEDICAL ENTOMOLOGY 

elongate, cylindrical, nearly colorless, and difficult to find. The easiest method 
of obtaining the larvae is to collect water with the bottom debris and soil 
from suspected breeding places, place it in small jars, and allow the debris 
to settle. The larvae, if present, can then be seen performing their peculiar 
movements. They swim about eellike with a side-to-side movement of the 
anterior part of the body, followed, each time, by a similar motion of the 
posterior part. The length of the larval life does not seem to be known. 




Fig. 752 (left). Head and mouth parts of Culicoidcs pulicatis L. fc, frontoclypeus; 
ga,galea; h, hypopharynx; 1, labium; Ire, labrum-epipharynx; m, mentum; md, mandible; 
p, palpus; ph, pharynx; s, stipes. (After Jobling, Bulletin oj Entomological Research.) 

Fig. 153 (right). Wings of Culicoides spp. (/) C. coc^erelli Coq. (2) C. diabolicus Hoff. 
(3) C. stellijcr Coq. (After Hoffman, American Journal oj Hygiene.) 

Pupation takes place in the water, on the surface of wet mud, at the water 
edge, or among algae. The pupa is elongate with conspicuous breathing trum- 
pets arising from the thorax (Fig. 154). The breeding habits and bionomics 
of this group are imperfectly known. 

Culicoides canithorax, C. melens, and C. dovei (Fig. 154) are serious pests 
in many places along the Atlantic seaboard. In the West Leptoconops torrens 
is an abundant species in the Sacramento and San Joaquin Valleys. Culicoides 
guttipennis and C. obsoletus (sanguisuga Coq.) are widely distributed in 
North America and are annoying pests. C. furens Poey is widely distributed 
along the southern, western, and northern shores of the Gulf of Mexico, 



OTHER BLOODSUCKING NEMOCEROUS FLIES 417 

southeastern Florida, the West Indies, Bahamas, and down the Atlantic coast 
to Brazil. 

The habits of the various species of Culicoides are not well known. Root 
and Hoffman (1937) record 33 species from North America and the Mexican 
highlands. They give very little information regarding their habits or bionom- 
ics. Johannsen (1943) lists 52 species from North America, Mexico, and 
the West Indies. 




Fig. 154. Life stages of the salt-marsh punkie, Culicoides dovei. (A} Adult. (#) Two 
of the eggs. (C) Full-grown larva. (D) Pupa. (All enlarged; after Dove and Hall.) 

OTHER GENERA 

The species of Leptoconops and iMsiohdea are less well known. The 
adults, so far as observed, are known to suck blood and are said to be very 
annoying. 

DISEASE 

The punkies affect man and animals by their bites and by acting as inter- 
mediate hosts of parasitic worms. To most people the bite is very annoying. 
It is usually accompanied by a prickling sensation; later a reddened area 



418 MEDICAL ENTOMOLOGY 

appears about the point of puncture, which usually swells, and is followed 
by an intolerable itching that may last for days. No serious effects follow if 
scratching is avoided. 

FILARIASIS: Sharp (1928), in the Cameroons, demonstrated that Culi- 
coides austeni serves as the intermediate host of Acanthocheilonema perstans. 
This filarial worm is widely distributed throughout tropical Africa and 
coastal parts of South America from Venezuela to Argentina. It is not known 
to cause any specific human disease. The microfilariac are found in the 
peripheral blood of man, gorilla, and chimpanzee. These are obtained when 
the fly takes blood. Within the gut of Culicoides austeni the rnicrofilariae are 
very active penetrating the gut wall within a few hours (six). About 24 hours 
later they are found in the thoracic muscles, where development proceeds. 
Six days later they migrate to the head and neck, and within a day or so more 
they are ready to emerge by way of the fly's proboscis. Though no actual 
passage of the larvae from the fly's proboscis through the human skin was 
observed by Sharp, it is believed that this species serves as an actual trans- 
mitter of this worm. Culicoides grahami has also been incriminated as a 
transmitter. Furthermore, in a dissection of 227 specimens of C. austeni caught 
in the wild, 7 per cent were found infected with the larvae of A. perstans. 

Buckley (1934) demonstrated the developmental cycle of Mansonella oz- 
zardi (Manson) in Culicoides jurens Poey. This filarial worm of man occurs 
in parts of South and Central America, Mexico, and certain parts of the West 
Indies. 

CONTROL OF SAND FLIES 

No successful methods have yet been devised for satisfactorily controlling 
these pests. Hull et al. (1939) attempted control of breeding in marshes and 
mangrove swamps by diking and pumping the areas dry. When successful, 
good control was obtained. The application of insecticides has not been ef- 
fective. The use of DDT in breeding areas might prove valuable. The treat- 
ment of screens, doors, and other woodwork about homes with a 5 per cent 
DDT in kerosene or other solvent has given some success in preventing 
these minute flies from entering homes. The use of repellents for personal 
protection is valuable. (See pp. 395-396.) 



OTHER BLOODSUCKING NEMOCEROUS FLIES 419 

REFERENCES 
SIMULIIDAE 

Bequaert, J. Medical and economic entomology. In Kept. Harvard-African 

expedition upon the African Republic of Liberia and the Belgian Congo, pp. 849- 

858. Cambridge, Mass., 1931. 
* . Notes on the black-flies or Simuliidae, with special reference to those 

of the Onchocerca region of Guatemala. In J. Bequaert et al., Onchocerciasis, 

Part III, 175-224. Cambridge, Mass., 1934. 
* . The black-flies or Simuliidae, of the Belgian Congo. Amer. Jl. Trop. 

Med. (Suppl.), 18: 116-136, 1938. 
Blacklock, D. B. The development of Onchocerca volvulus in Simulium damno- 

sum. Ann. Trop. Med. Parasit., 20: 1-48, 203-218, 1926. 
Cameron, A. E. The morphology and biology of a Canadian cattle-infesting 

black-fly (Simulium simile Mall.). Dept. Agr. Dom. of Canada, Bull. 5, n.s. 

(Tech.), 1922. 
Ciurea, T., and Dinuflescu, G. Ravages causes par la mouche de goloubatz en 

Ron man ie; ses attacques contre les animaux et contre 1'homme. Ann. Trop. 

Med. Parasit., 18: 323-342, 1924. 
Dyar, H. G., and Shannon, R. C. The North American two-winged flies of the 

family Simuliidae. Proc. U.S. Nat. Mus., 69, art. TO (No. 2636), 1927. 
Edwards, I 1 ". W. On the British species of Simulium. I. The adults. Bull. 

Ent. Res., 6: 23-42, 1915. II. The early stages; with corrections and additions 

to part I. Ibid., u: 211-246, 1920. 
. Simuliidae. In Diptera of Patagonia and south Chile, Part 2, fasc. 4, 

121-154. London, 1931. 
Friederichs, K. Untersuchungen iiber Simuliiden. Zeit. Angew. Ent., 6: 16-83, 

1920. II. Theil. Ibid., 8: 31-92, 1922. 
Gibbins, E. G. On the mate terminalia of Simuliidae. Ann. Trop. Med. Parasit., 

2 9 : 3 1 7~3 2 5 I 935- 

. Congo Simuliidae. Ibid., 30: 131-150, 1936. 

HofTman, C. C. Investigaciones sobre la transmission de la onchocercosis de 

Chiapas. Anales Inst. Biol. Mexico, i: 59-62, 1930. 
. Los simulidos de la region onchocercosa de Chiapas. Ibid., pp. 293-306, 

1930. 
. Ueber Onchocerca in Suden von Mexiko und die Wietercnwicklung ihrer 

Mikrofilarien in Eusimulium mooseri. Arch. SchifT. Trop. Hyg., 34: 461-472, 

1930. 
. Los simulidos de la region onchocercosa de Chiapas. Secunda parte. Los 

estados larvales. Anales Inst. Biol. Mexico 2: 207-218, 1931. 
Jobbins-Pomeroy, A. W. Notes on five North American buffalo gnats of the genus 

Simulium. U.S. Dept. Agr., Bull. 329: 1-48, 1916. 



420 MEDICAL ENTOMOLOGY 

Johannsen, O. A. Aquatic Diptera. I. Cornell Univ. Agr. Exp. Sta., Mem. 164: 

56-64, 1934. 
Johnson, E. P., Underbill, G, W., Cox, J. A., and Threlkeld, W. L. A blood 

protozoan of turkeys transmitted by Simulium nigroparvum (Twinn). Amer. 

Jl. Hyg., 27: 649-665, 1938. 
Krafchick, Bernard. The mouthparts of blackflies with special reference to 

Eusimulium lascivum Twinn. Ann. Ent. Soc. Amer., 35: 426-434, 1942. 
Lutz, A. Contribute para o conheicmento das especies brazileiras do genero 

"Simulium." Mem. do Instit. Oswaldo Cruz, 2: 213-267, 1910. 
Malloch, J. R. American black-flies or buffalo-gnats. U.S. Dept. Agr., Bur. Ent., 

Tech. Ser. 26, 1914. 
Meillon, B. de. On the Ethiopian Simuliidae. Bull. Ent. Res., 21: 185-200, 

1930. 
O'Roke, E. C. A malaria-like disease of ducks caused by Leucocytozoon anatis 

Wickware. Mich. Univ. Sch. Forest. Conser., Bull. 4, 1934. 
Pinto, C. Simuliidae do America Central e do Sul. 7" Reun. Soc. Arg. Pat. Reg. 

Norte, 60: 661-763, 1931. 
*Puri, I. M. On the life-history and structure of the early stages of Simuliidae. 

I, II. Parasitology, 17: 295-369, 1925; 18: 160-167, 1926. 
. Studies on Indian Simuliidae. Ind. Jl. Med. Res., 19: 883-915, 1125- 

1143, 1932; 20: 504-532, 803-812, 813-817, 1933; 21 : 1-16, 1933. 
Rempel, J. G., and Arnason, A. P. An account of three successive outbreaks of 

the black-fly, Simulium arcticum. Sci. Agr., 27: 428-445, 1947. 
**Smart, John. The classification of the Simuliidae (Diptera). Trans. Roy. Ent. 

Soc. Lond., 95: 463-532, 1945. 
**Solanes, M. P., Vargas, L., Mazzoti, L., Rojas, A. G., and Riveroll, B. Oncocer- 

cosis. Mexico, D.F., 1948. 
Stokes, J. H. A clinical, pathological, and experimental study of the lesions 

produced by the bite of the black-fly (Simulium venustum). Jl. Cutaneous 

Dis., 22: 751-769, 830-856, 1914. 

Strong, R. P. Onchocerciasis in Guatemala. Science, n.s., 73: 593-594, 1931. 
Tonnoir, A. Australian Simuliidae. Bull. Ent. Res., 15: 213-255, 1925. 
*Twinn, C. R. The blackflies of eastern Canada (Simuliidae, Diptera). Can. 

Jl. Res., D, 14: 97-150, 1936. 
*Vargas, Luis. Simulidos del Nuevo Mundo. Inst. Salub. y Enferm. Trop. 

Monograph i, 1945. 
* , Palacios, A. M., and Najera, A. D. Simulidos de Mexico. Rev. Inst. Salub. 

y Enferm. Trop., 7: 101-192, 1946. 
**Wilhelmi, J. Die Kriebelmuckenplage. Jena, 1920. 
*Wu, Y. Fang. A contribution to the biology of Simulium (Diptera). Mich. 

Acad. Sci. Arts Let., 13: 543-599, 1931. 



OTHER BLOODSUCKING NEMOCEROUS FLIES 421 

CERATOPOGONIDAE (HELEIDAE) 

Bequacrt, J. Report of an entomological trip to the Truxillo Division, Honduras, 

to investigate the sand-fly problem. i3th Ann. Kept., United Fruit Co., Med. 

Dept., pp. 193-206, 1925. 
Carter, H. F. A revision of the genus Leptoconops Skuse. Bull. Ent. Res., 12: 

1-28, 1921. 
, Ingram, A., and MacFie, J. W. S. Observations on the Ceratopogonine 

midges of the Gold Coast, with descriptions of new species. Ann. Trop. Med. 

Parasit., 14: 187-210, 211-274, 309-331, 1920; 15: 177-212, 1921. 
Dove, W. E., and Hall, D. G. Dikes and automatic tide gates in control of sand- 
flies and salt marsh mosquitoes. J. Parasit., 20: 337-338, 1934. 
Edwards, F. W. On the British biting midges (Diptera, Ceratopogonidae). 

Trans. Ent. Soc. Lond., 74: 389-426, 1926. 
Fiilleborn, F. The "blinding filaria" of Guatemala (Onchocerca caecutiens 

Brumpt, 1919). Proc. Internal. Conf. on Health Problems in Trop. Amer., 

pp. 241-256, 1924. 
Goetghebuer, M. Ceratopogoninae de Belgique. Mem. Mus. R. Hist. Nat. Belg. 

8 (3): 1-116, 1920. 
. Heleidae (Ceratopogonidae). In E. Lindner, Die Fliegen, Lieferung 77, 

78: 1-133, Stuttgart, 1933-1934. 
Hoffman, W. A. A review of the species of Culicoides of North and Central 

America and the West Indies. Amer. }1. Hyg., 5: 274-301, 1925. 
Hull, J. B., Dove, W. E., and Platts, N. G. Experimental diking for control of 

sandfly and mosquito breeding in Florida salt-water marshes. Jl. Econ. Ent., 

32: 309-312, 1939. 
Ingram, A., and MacFie, J. W. S. Notes on some African Ceratopogoninae 

species of the genus Lasiohelea. Ann. Trop. Med. Parasit., 18: 377-392, 1924. 
, and MacFie, J. W. S. Diptera of Patagonia and south Chile. II. Fasc. 4. 

Ceratopogonidae, pp. 155-232, 1931. 
Jobling, B. The structure of the head and mouth parts of Culicoides pulicaris L. 

Bull. Ent. Res., 18: 211-236, 1928. 
*Johannsen, O. A. A generic synopsis of the Ceratopogonidae (Heleidae) of the 

Americas, a bibliography, and a list of the North American species. Ann. Ent. 

Soc. Amer., 36: 763-791, 1943. 
Kieffer, J. J. Chironomidae. In P. Wytsman, Genera Insectorum, Fasc. 42. 

Brussels, 1906. 
. Faune de France, n. Dipteres (Nematoceres piqueurs); Chironomidae, 

Ceratopogoninae. Paris, 1925. 
Lutz, A. Contribu^a para o estudion das "Ceratopogonias" haematofagas encon- 

tradas no Brazil. MIL Mem. do Instit. Oswaldo Cruz, 4: 1-33, 1912; 5: 45- 

73, 1913; 6: 81-99, 1914. 



422 MEDICAL ENTOMOLOGY 

Macfie, J. W. S. The genera of Ceratopogonidae. Ann. Trop. Med. Parasit., 

34: 13-30, 1940. 
Malloch, J. R. The Chironomidae, or midges, of Illinois, with particular reference 

to the species occurring in the Illinois River. Bull. State Lab. Nat. Hist., 10, 

art. VI: 1915; u, art. IV: 305-363, 1915. 
Painter, R. H. The biology, immature stages, and control of the sandflies (biting 

Ceratopogoninae) at Puerto Castilla, Honduras. i5th Ann. Rept., United Fruit 

Co., Med. Dept., pp. 245-262, 1927. 
Robles, R. Onchocercose humaine au Guatemala produsiant la cecite et "1'erysipele 

du littoral" (Erisipela de la costa). Bull. Soc. Path. Exot., 12: 442-463, 1919. 
*Root, R. M., and Hoffman, W. A. The North American species of Culicoides. 

Amer. Jl. Hyg., 25: 150-176, 1937. 
Sharp, N. A. D. Development of Microfilaria perstans in Culicoides grahami; 

a preliminary note. Trans. Roy. Soc. Trop. Med. Hyg., 21: 70, 1927. 
* . Filaria perstans; its development in Culicoides austeni. Ibid., pp. 371 

396, 1928. 
*Thomsen, Lillian C. Aquatic Diptera. V. Ceratopogonidae. Cornell Univ. 

Agr. Exp. Sta., Mem. 210: 57-80, 1937. 



CHAPTER XIV 



The Tabanidae and Rhagionidae: 

Horseflies, Deer Flies, Clegs, 
Green-headed Flies; Snipe Flies 



THE family Tabanidae is a very large one. Between two thousand and 
twenty-five hundred species have been described from the world; over 
three hundred species are recorded from North America. The adults are of stout 
build (Fig. 155) ; bristles practically absent; eyes large and prominent (contigu- 



7 




Fig. 755. Tabanus atratus Fabr, Female at left; male at right. 

ous in nearly all the males) and usually brilliantly colored (the colors disappear 
after death) ; antenna with the third joint annulated (Fig. 51 5) but never with 
a style; proboscis well developed, short (Tabanus, Haemafopota) , rather long 



4 2 4 MEDICAL ENTOMOLOGY 

.^Chrysops), or very long (certain Pangonia spp.); mouth parts adapted for 
piercing (Fig. 156) ; venation (Fig. 56) rather characteristic, the costal vein 
extending all around the wing. The squamae are large and the pulvilli and 
empodia are padlike. 

In general the adults are robust, rather compact-looking flies; the powerful 
wings, stout depressed abdomens, and large, rounded heads give them the 
appearance of vigor and activity. They range in size from about that of the 
housefly (some Chrysops species) to the large Tabanus species with a wing 
expanse of over two and one-half inches. The females of the great majority of 
the species are bloodsucking in habit, while the males peacefully take only 
plant juices, nectar, excreta of some other insects, or any available liquids con- 
taining nutritive material. The females have a wide range of hosts, the larger 
mammals, especially our domestic animals, being most frequently attacked. 
Certain species are known to attack crocodiles and others obtain blood from 
sea turtles, biting between the plates on the back. In many parts of the world 
they are serious pests of livestock, and cattlemen frequently suffer serious 
losses from outbreaks of these flies. Webb and Wells (1924) state that a 
medium-sized tabanid requires 8 to TO minutes to feed and takes about 0.125 
cubic centimeters of blood; Stone (1930) estimates that such a fly takes nearly 
0.2 cubic centimeters for a meal. It will thus be seen that when these flies are 
very abundant the daily loss of blood must be a serious drain. 

The flies are lovers of sunlight, warmth, and moisture. They are attracted 
to moving objects, and species of Tabanus and Chrysops consistently attack 
man. During dark, cloudy days, or cool, rainy weather they remain inactive, 
resting quietly in secluded places. Their range of flight must be considerable, 
though no one has apparently investigated this phase of their activities. Mac- 
Creary (1940) reports the collection of adults at light traps located 3 to 8 
miles offshore. They are much more abundant near their breeding grounds 
swamps, marshes, irrigated land, river bottoms, along the margins of rivers 
and lakes, and in similar places than in the open, drier country. The length 
of the adult life is apparently not very long, probably not over four weeks to 
two months as shown by Stone (1930) from his consistent weekly collecting 
data. In Louisiana Jones and Bradley (1916 and 1917) present somewhat similar 
data, which indicate a longer season for the activity of the adults of certain 
species (Tabanus vicarius, T. lineola, Chrysops flavidus). In the region of 
central New York and no doubt elsewhere (as indicated by Jones and Bradley 
in Louisiana), the emergence and flight activity of the different species take 
place at rather definite periods of the year. As a result, the maximum abun- 
dance of any one species may be concentrated in a rather short period (as 



THE TABANIDAE AND RHAGIONIDAE 



425 



Tabanus pumilus in midsummer) or somewhat prolonged in the case of those 
species that normally emerge later in the season. 

THE MOUTH PARTS OF A HORSEFLY (Chrysops sp.) : In the horsefly 
the mouth parts project downward and look like a cylindrical sac with a pair 




-Hphy 



Lm 



Fig. 156. Frontal view of the head and mouth parts of a horsefly (Chiysops univitta- 
tus). The mouth parts are withdrawn from the labium in order to show them separately. 
Ant, antenna; Clp, clypeus; Hphy, hypopharynx; Lb, labrum; Lm, labium (the dotted 
line points to the tip, usually called the labella); rnd, mandible; MX, maxilla; MxPlp, 
maxillary palpus. 

of palpi overlapping it (Fig. 156). The saclike appearance is due to the en- 
largement of the labium, which is hollowed out on its anterior face and 
terminates in two lobes, the labella. Within this hollow lie the mouth parts 
for piercing. These consist of a long dagger-shaped labrum, a pair of saber- 
shaped mandibles, a pair of bladelike maxillae with their palpi, and a long 



426 MEDICAL ENTOMOLOGY 

tapering stylet, the hypopharynx. The details of these structures and their 
muscles are shown and explained in Fig. 157. The labium is a large, thick 
organ, deeply grooved along its anterior face, and terminates in the two broad 
lobes called the "labella." In the normal position the labella are closed, but 




Fig. 757. Mouth parts of a horsefly (Chrysops univittatus] . Left: Labrum and hypo- 
pharynx showing their relationship and their connection to the head and some of the 
muscles (the hypopharynx is slightly withdrawn in order to show it more clearly). 
Center: The right mandible with muscles in place. Right: The left maxilla with its 
muscles. C, cardo; Clp, clypeus; Dm, dilator muscle of the food pump; DSp, dilator 
muscle of the salivary syringe; Em, extensor muscle of the maxilla; Fp, food pump or 
pharyngeal pump; Hphy, hypopharynx; Lm, labrum; LmM, labral muscle; Mi, Ms, Ms, 
muscles that move the mandible; md, mandible; Mt. mouth; MX, maxilla; MxPlp, 
maxillary palpus; Rm, retractor muscle of maxilla; Sg, common salivary duct leading to 
salivary syringe (note the two valves, one at entrance to syringe and one at exit); Sp, 
salivary syringe; St, stipes. 

they can be spread apart like broad, soft pads. The posterior portions of the 
labella are firmly united, but the anterior halves are separated by a deep 
median cleft. The undersurface of each lobe is traversed by close-set channels 
called "pseudotracheae." 
The action of these mouth parts is difficult to determine. The probable 



THE TABANIDAE AND RHAGIONIDAE 427 

action is as follows : the fly spreads its soft, padlike labella on the skin, drives 
the mandibles into the skin, and by means of the powerful mandibular muscles 
rips it. By continuing such action the mouth parts, except the labium, are 
driven deeper and deeper into the flesh. The barbed ends of the maxillae prob- 
ably act as holdfasts, and the mandibles by muscular action can be twisted 
in the wound. By this means blood soon flows rapidly and is pumped by 
the food pump up the channel made by the labrum and hypopharynx. The 





Fig. 158. Egg masses of horseflies. (A) Egg mass of Chrysops sp. 
(B) Egg mass of Tabanus phaenops. (B after Dotcn.) 

salivary secretion is forced into the wound by the salivary pump. This secre- 
tion is said to possess an anticoagulin and an irritant to facilitate and increase 
blood flow. 

LIFE HISTORY: As the larval life of practically all our common species 
is passed in water, wet soil, or semiaquatic conditions, the eggs are laid in the 
vicinity of such situations. The places of oviposition may be classified as fol- 
lows (according to Stone, 1930) : 

i. Foliage or other objects over shallow, quiet water, edge of shallow 
pools, lakes. 



428 MEDICAL ENTOMOLOGY 

2. Foliage or other objects in relatively deep water at some distance from 
shore, or on ledges, or rocks, over deep water. 

3. Stones or other objects projecting over flowing streams. 

4. Vegetation, as leaves or trunks of trees, over either moist or even quite 
dry soil. 

The eggs are deposited in masses (Fig. 158), varying in number from 100 
to 800 eggs. The species of Chrysops usually place their eggs in a single layer 
(Fig. 158 A), though C. celer and C. piJ(ei place theirs in double tiers; those of 
Tabanus are generally laid in several layers (Fig. 158 B). The egg masses are 
protected by a gluey, waterproof covering, placed on them by the female when 




Fig- 159- A sagittal sectional view of the head of a tabanid larva to show the relation 
of the mouth parts to the pharynx. C, canal through the mandible; CB, cephalic brush 
of spines; DM, dilator muscle of the salivary pump; DPh, dilator muscles of the pumping 
pharynx; E, esophagus; Lm, levator muscle of the mandible and maxilla and the cephalic 
brush; LbPlp, labial palpus; Md, mandible; MX, maxilla; Ph, pharynx; Pip, maxillary 
palpus; S, common salivary duct; Sm, salivary duct from pump to labium; Sp, salivary 
syringe; T, anterior extension of the tentorium; Ten, tentorium; V, valves of the salivary 
pump. (Redrawn and modified from Cameron.) 

in the act of oviposition. The egg stage, normally, lasts but a short time, 
usually not more than 5 to 7 days, though it may be prolonged by cool, un- 
favorable weather. All of the eggs of a mass hatch at about the same time, and 
the larvae immediately drop to the water or the ground beneath. 

The larvae are primarily carnivorous and cannibalistic; some species are un- 
doubtedly saprophagous (many Chrysops spp.). The larval mouth parts are 
adapted for piercing and extracting the contents of their victims (Fig. 159). 
The length of the larval life varies considerably. In most of our North Ameri- 
can species the larval stage requires from 9 to n months though, undoubtedly, 
the amount and availability of food determines, to a large extent, the time of 
pupation. Under laboratory conditions Webb and Wells reared Tabanus 
punctifer from the egg to the adult stage in less than two years. The rearing 



THE TABANIDAE AND RHAGIONIDAE 



429 



conditions were abnormal and, in nature, the larval growth is completed 
probably in less than a year. Stone (1930), Schwardt (1936), Logothetis (un- 
published thesis), and others have reared considerable numbers of Tabanidae. 
The average larval life of those reared was about n to a little over 12 months, 
while the pupal period varied from five days to two or three weeks. However, 
certain larvae of the species required nearly two years (as Tabanus vicarius 
in its northern range). 




Fig. 160. Larvae of Tabanidae. (/) Chrysops discalis Will. (2) C. excitans 
Walk. (3) C. julvaster OS. (4) Siphon of C. excitans. (5) Tabanus rcinwardtii 
Wied. (6) T. septcntrionalis L. (From Cameron, Bulletin of Entomological 
Research.) 

The larvae of Tabanidae possess n body segments exclusive of the small 
retractile head (Fig. 160). The body is cylindrical, tapering toward both ends, 
usually striated longitudinally, and with a single posterior siphon. The siphon 
is borne on the dorsal portion of the anal segment. It can be telescoped within 
the anal segment and bears on its tip the openings of the respiratory system 
(metapneustic). In addition, the presence of Graber's organ within the tenth 
and eleventh segments (readily seen in most tabanid larvae) will distinguish 
these larvae from all others. The organ consists of a scries of capsules, each 



430 MEDICAL ENTOMOLOGY 

containing a pair of minute, black pyriform bodies, lying in a pyriform sac 
directly beneath the integument of the tenth and eleventh segments. In the 
case of Goniops chrysocoma, the larva has a club-shaped body, swollen pos- 
teriorly, and the striations are overshadowed by the mammillated parts of the 
integument; Graber's organ is not easily seen and no distinct siphon is visible. 
When the larvae are mature they migrate to drier, rather compact soil where 
they pupate. The pupal period is rather short, ranging usually from one to 
three weeks. 

CLASSIFICATION 

The family Tabanidae contains a large number of genera, at least over sixty. 1 
Surcouf (1921) presents a key to the genera of the world; Krober and Bequaert 
give us a review of most of the African species; Hine (1903) treats of the 
North American species; and other workers give incomplete accounts of the 
species from different parts of the world. Bequaert (1924) states that in Amer- 
ica, north of Panama, there are over 334 species distributed among 21 genera; 
of this number 71 belong to the genus Chrysops and 206 to the genus Tabanus; 
the other genera contain from i to 18 species. Brennan (1935) gives an excellent 
account of the subfamily Pangoniinac and Stone (1938) that of the subfamily 
Tabaninae for North America. Philip (1947) attempts a rather new classifica- 
tion of the Tabanidae, dividing the family into the normal subfamilies and 
these into tribes (3 tribes in the Pangoniinae; 4 tribes in the Tabaninae) and 
recognizes 27 genera with 474 species for North America north of Mexico. 
However, the following brief key will aid in placing the more common species 
in their correct genera. For the identification of the larvae, Stone (1930) gives 
preliminary keys to the immature stages of the North American species 
(Chrysops, Tabanus, and Goniops spp.) which he knew. 

KEY TO SOME OF THE NORTH AMERICAN GENERA 

1. Hind tibiae with spurs at the tips; ocelli usually present 

Subfamily Pangoniinae 2 

Hind tibiae without spurs at their tips; ocelli absent 

Subfamily Tabaninae 7 

2. Third segment (the flagellum) of antenna with 5 distinct annuli 3 

Third segment of antenna with 8 distinct annuli 4 

3. Pedicel (2nd segment) of antenna about one-half as long as the first seg- 

ment (the scape) Silvius 

1 Enderlein (1922, 1923) recognizes over 150 genera from the world, many of them 
with but one or two species. 



THE TABANIDAE AND RHAGIONIDAE 431 

Pedicel more than one-half as long as the scape, often nearly as long; 
wings usually infuscated, picturelike Chrysops 

4. Eyes of females acutely angulate above; basal portion of wing infuscated 

Goniops 

Eyes of female not angulate above; wings of uniform color 5 

5. Maxillary palpi short, stubby, about equal in length to the proboscis 

Apatolestes 

Maxillary palpi slender, shorter than proboscis 6 

6. Cell R 5 petiolate EsenbecJ^ia 

Cell R 5 open, not petiolate Stonemyia 

7. Third antennal segment with 4 annuli; wings gray, with small white 

spots Haematopota 

Third antennal segment with 5 annuli; wing pattern, if any, not as 
above 8 

8. Basal part of third antennal segment without a dorsal projecting tooth; 

eyes bare; wing with at least a subapical brown spot Diachlorus 

Basal part of third antennal segment with or without a dorsal projecting 
angle; if angle is present eyes are bare (not pilose) 9 

9. Eyes distinctly pilose; ocellar tubercle absent; eyes of female with a single 

diagonal, purple line (usually present even in dried specimens). Palpi 

not black and abdomen without a dorsal stripe Atylotus 

Eyes pilose or bare but without the diagonal line; either the palpus black 

or the abdomen with a narrow, dorsal stripe Tabanus 

Stcnotabanus 

NOTES ON SOME OF THE GENERA: The genus Tabanus contains a 
vast assemblage of species, over a thousand being listed from the world; Be- 
quaert (1924) reports over two hundred from North America north of Pa- 
nama, while Stone (1938) recognizes 124 species in North America north of 
Mexico. Most of the species are large (Fig. 155), stout, vigorous fliers and 
readily attack man and animals. 

Chrysops is the next largest genus, the species being world-wide in distribu- 
tion; over eighty species are recorded from North America. They are com- 
monly called "deer flies." The species are rather small (Fig. 161). The wings 
are clear except for a broad, dark area along the anterior margin of the wing 
and a broad, dark band across the wing at the level of the discal cell or just 
beyond it; the apex may be clear or infuscated. They readily attack man and 
are often extremely annoying. Most of the species are partial to low-lying 
marshy or swampy woods. 

Silvius is a small genus of which we have six species in North America. 



432 MEDICAL ENTOMOLOGY 

Representatives of this genus occur abundantly in the Australian region. 

The species of the genus Haematopota are most abundant in the Ethiopian 
and Oriental regions, though they occur in all parts of the world. Only two 
species are recorded by Stone (1938) as occurring in North America. 

In the genus Pangonia the eyes are more or less broadly separated in the 
female, whereas in the male they may be contiguous or separated. Ocelli are 
usually present though they may be absent. The proboscis is of variable length, 
but it is generally longer than the head and frequently very long. The sixth 
longitudinal vein is straight. This genus has been broken up into a number 
of genera of rather doubtful validity. 

The genus Diachloms is practically restricted to South America. One species, 
>. jerrugatus Fabr., is known from North America (Delaware to Florida 
and Mexico to Brazil). 

RELATION TO DISEASE 

In addition to the effects of their bites and the loss of blood, man and animals 
suffer from certain diseases that are distributed by tabanids either mechanically 
or as intermediate hosts. 

FILARIASIS 

Loa loa Cobbold is a filarial worm that has been recovered at various times 
from man for over a hundred years. The earliest observations (1770-1825) 
were on Negroes recently imported into the West Indies. Later this worm was 
found in its indigenous territory in West Africa. At present it is widespread 
along the west coast from Nigeria and the Cameroons down to Angola and 
inland to central tropical Africa and possibly to Uganda. The mature female 
worm measures from 50 to 70 mm. in length and about 0.5 mm. in maximum 
width; the male from 30 to 34 mm. in length to about 0.4 mm. in width. They 
are found in the subcutaneous tissues of man where they migrate back and 
forth. They have been found in various parts of the body but seem to have a 
predilection for the head, especially the eye (hence often called the "eye 
worm"). Frequently these worms appear to produce swellings, the so-called 
"Calabar swellings," which may become as large as half a goose egg. These 
swellings are generally painless, hot, and disappear in a few days. What 
relation the worm bears to the swellings has not, apparently, been deter- 
mined. 

The females discharge microfilariae in the passages made during their migra- 
tions. These reach the peripheral blood vessels, where they are found during 



THE TABANIDAE AND RHAGIONIDAE 433 

certain parts of the day (9 A.M. to 2 P.M.), hence were called Micro filaria diurna 
by Manson. On epidemiological grounds Manson (1895) suggested that a spe- 
cies of mangrove fly (Chrysops dimidiata v. d. Wulp) was the intermediate 
host. Leiper (1912, 1913) and Kleine (1915) added certain experimental evi- 
dence in support of this view. However, the Connals (1921 and 1922) com- 
pletely elucidated the entire life cycle of this worm. From dissections of wild 
specimens (2283) of Chrysops dimidiata and C. silacea they found 0.96 per 
cent infected with filariae. Experimentally they showed that these flies take 
up the microfilariae while feeding; the microfilariae then bore their way out 
of the gut and lodge in the thoracic and abdominal muscles; here further de- 
velopment takes place and in 10 to 12 days after the infective meal mature 
larvae appear in the proboscis. The fly is now ready to infect new hosts. Most 
of the larvae leave the fly at its first meal, though it may remain capable of 
infecting new hosts for at least five days. The Connals were able to infect, 
experimentally, guinea pigs, rabbits, and a monkey. The two tabanids, C. dimi- 
diata and C. silacea, are strictly diurnal in their feeding habits and feed com- 
monly on man. In all probability other species of bloodsucking flies will be 
found capable of transmitting this filarial worm. 

TULAREMIA 

Tularemia is an infectious disease caused by Bacterium tularensc (Pasteu- 
rella tularensii) . Primarily it occurs in nature as a plaguelike disease of rodents, 
especially rabbits and hares. It is transmitted to man by various bloodsucking 
insects (see Chapter in). It is of interest here because Francis (1919, 1920) first 
recognized the identity of "deer-fly fever" and the "plague-like disease of 
rodents." By careful experiments Francis and Mayne (1921) were able to 
demonstrate the agency of Chrysops discalis (Fig. 161) in disseminating the 
disease from infected to healthy guinea pigs and rabbits. They found the 
method of transmission was purely mechanical, though the fly could remain 
infective as long as 14 days. They found that practically all the flies did remain 
infective at least as long as eight days after their infecting meals. They also 
demonstrated that numerous human cases of tularemia were due to the bite of 
this fly, the fly obtaining the bacterium from jack rabbits and transmitting it 
to man. Cases due to the bite of Chrysops discalis have been reported from 
Utah, Idaho, Wyoming, Colorado, Nevada, Oregon, and Montana. 

ANIMAL DISEASES 

The species of Tabanidae are extremely annoying and injurious to live- 
stock and many of the larger game animals. Not only do these animals suffer 



434 MEDICAL ENTOMOLOGY 

from their bites and consequent loss of blood, but the flies frequently dis- 
tribute pathogenic organisms from one animal to another. This is due to the 
fact that frequently the flies, not being allowed to complete their blood meal 
on one host, immediately attack another. In this way they may transmit, 
mechanically, any organism on the proboscis obtained from the previous host. 
The principal types of disease transmitted in this manner are those in which 
the virulent organisms are present, in large numbers, in the peripheral blood 
and somewhat resistant to short exposures. to the air. Here are found such 
diseases as anthrax, trypanosomiasis, hemorrhagic septicemia, etc. 




Fig. 161. Chrysops discalis Will. (After Francis.) 

ANTHRAX: A few investigators have demonstrated the possibility of the 
mechanical transmission of this disease from animal to animal by biting flies, 
principally Tabanidae. Mitzmain (1914) proved in a number of controlled 
experiments that Tabanus striatus could transmit anthrax from infected to 
healthy animals. This was accomplished by the method of interrupted feed- 
ing, the fly feeding on a heavily infected guinea pig and then transferring 
within a short time to a healthy one. If flies were allowed to feed on infected 
guinea pigs a short time after their death and were then transferred to healthy 
pigs, no infection resulted. Though his experiments were few in number, he 
demonstrated the possibility of species of Tabanidae distributing the disease 
in nature. Morris (1918) obtained a high percentage of infection by feeding 



THE TABANIDAE AND RHAGION1DAE 435 

a Tabanus sp. on dying guinea pigs (from four hours before death till 20 
minutes after death) and then immediately feeding them on healthy pigs. 
Herms states that physicians have told him of the infection of man (malig- 
nant pustule) by the bites of horseflies. 

TRYPANOSOMIASIS: Various species of trypanosomes have been shown 
to be transmitted mechanically on the proboscis of different species of horseflies. 
It would be entirely possible for almost any bloodsucking tabanid to do 
this provided it could feed for a brief period on an infected animal and then 
be immediately transferred to a susceptible host. The trypanosomes are in- 
jected, provided they are present within or on the proboscis in a viable condi- 
tion, into the new host at the time of biting. Some of the important trypano- 
somes that have been shown capable of being transmitted in this manner are 
T. evansi (causative agent of surra), principally by species of Tabanidae and 
also by Stomoxys calcitrant and S. nigra (as this trypanosomc has no known 
intermediate host in which a cyclical development takes place, the only known 
method of transfer is by biting flics) ; T. soudanense (believed to be only a 
variety of T. evansi) , which causes a chronic disease, eldcbab, of camels and 
is transmitted by horseflies; and T. hippicum, which causes a trypanosomiasis 
of mules and horses in South America and parts of Central America and is 
transmitted by Tabanus importunus (Colombia and Venezuela). In Panama, 
Dunn (1932) and Clark and Dunn (19^) demonstrated that the vampire 
bat (Desmodits rotund its miirinits) is the important vector. T. annamense, 
another horse-infecting trypanosome in Annam and Tonkin, is transmitted 
by tabanid species; T. cquiperditm, the causative agent of dourine in horses, 
has been shown to be capable of transmission by bloodsucking flics, Tabanus 
nemoralis and Stomoxys calcitrans (this trypanosome is normally transmitted 
by direct contact of mucous surfaces as in coitus; it has no known intermediate 
host) . 

CONTROL 

No successful methods of controlling horseflies have as yet been devised. 
The reduction of possible breeding areas by drainage is suggested, and Webb 
and Wells (1924) point out that no breeding took place in well-drained 
areas. Recently Logothetis and Schwardt (1948) found numerous larvae of 
Tabanus vicarius (costalis), one of our most abundant horseflies, in dry 
upland soil such as pasture land, cornfields, and cabbage fields. As many 
tabanids have the habit of flying over pools, dipping their bodies into the 
surface of the water, Portchinsky suggested the application of kerosene oil 



436 MEDICAL ENTOMOLOGY 

to the surface of pools favored by the flies. He tried several experiments with 
most gratifying results. The oil would have to be applied when the flies are 
abundant and at various periods to meet the time of emergence of the dif- 
ferent species. Webb and Wells record an egg parasite, Prophanurus emersoni 
Girault, as an effective check on the breeding of Tabanus punctijer. 




Pig, 162. Symphoromyia atripes. (After Ross, Annals of the Entomological Society of 
America.) 

THE RHAGIONIDAE (LEPTIDAE) 
The Snipe Flies 

The Rhagionidae consists of rather small, or medium-sized, dark flies, found 
commonly in woodlands, especially near moist places. Unlike the horseflies, 
they are rather sluggish and easily captured. Both adults and larvae are preda- 
ceous. However only two genera are known to be bloodsucking in habit, 
Symphoromyia in North America and Spaniopsis in Australia. The species 
of Symphoromyia can be recognized by the kidney-shaped third antennal seg- 



THE TABANIDAE AND RHAGIONIDAE 437 

ment. About 25 species of Symphoromyia are known from North America 
and most of these species are from the mountainous regions of the West. Prac- 
tically none of these have been taken in lowlands or valleys. 

S. hirta Johnson is a large species (7.5 mm. in length) and is widely distrib- 
uted in North America. Its flight habits resemble those of Chrysops spp. and 
its bite is rather severe. Mills (1943) describes an outbreak of this fly in the 
mountains of southwest Montana, the flies attacking viciously and being 
very troublesome to game animals. S. atripes Bigot (Fig. 162) is prevalent in 
parts of the mountains of western America and it is recorded as causing as 
much or more annoyance than mosquitoes. It attacks quietly and Ross (1940) 
records it as extremely annoying in the mountains (above 5000 ft.) in British 
Columbia. S. pachyceras Will, and S. kjncaidi Aid. are also reported as blood- 
sucking in habit in parts of the Pacific coast area. 

As far as known, the biology or breeding habits of none of our blood- 
sucking species are known. Other species of rhagionids are known to breed 
in moist soil where there is decaying vegetation 

REFERENCES 

Bequaert, J. Tabanidae. In Contributions from the Harvard Institute of Tropical 
Biology and Medicine. No. iv, Medical rept. of the Hamilton Rice 7th ex- 
pedition to the Amazon, pp. 214-235. Cambridge, Mass., 1926. 

. Tabanidae. In Rept. of the Harvard expedition upon the African Re- 
public of Liberia and the Belgian Congo, pp. 858-971. Cambridge, Mass., 
1931. (Extensive account of the Tabanidae of the Congo region.) 

*Brennan, J. M. The Pangoniinae of Nearctic America. Univ. Kansas Sci. Bull., 
36: 249-401, 1935. 

Bromley, S. W. The external anatomy of the black horse-fly Tabanus atratus Fab. 
Ann Ent. Soc. Amer., 19: 440-460, 1926. 

Cameron, A. E. Bionomics of the Tabanidae (Diptera) of the Canadian prairies. 
Bull. Ent. Res., 17: 1-42, 1926. 

Connal, A., and Connal, S. A preliminary note on the development of Loa loa 
(Guyot) in Chrysops silacea (Austen). Trans. Roy. Soc. Trop. Med. Hyg., 
15: 131-134, 1921. 

, and Connal, S. The development of Loa loa (Guyot) in Chrysops silacea 

(Austen) and in Chrysops dimidiata (van d. Wulp). Ibid., 16: 64-89, 1922. 

Enderlein, G. Eine neues Tabanidensystem. Mit. Zool. Mus., Berlin, 10, 2: 333- 
351, 1922. 

*Francis, E. Arthropods in the transmission of tularaemia. Trans. 4th Internat. 
Cong. Ent. (1928), II: 929-944, 1929. 

, and Mayne, B. Experimental transmission of tularaemia by flies of the 



438 MEDICAL ENTOMOLOGY 

species Chrysops discalis, U.S. Pub. Hlth. Serv., Hyg. Lab., Bull. 130: 8-16, 
1922. 

Hine, J. S. Tabanidae of Ohio with a catalogue and bibliography of the species 
from America north of Mexica. Ohio State Acad. Sci., Spl. Paper No. 5, 1903. 

- . Tabanidae of the western United States and Canada. Ohio State Univ., 
Contrib. Dept. Zool. and Ent., No. 21: 217-248, 1904. 

- . Habits and life-histories of the flies of the family Tabanidae. U.S. Dept. 
Agr., Bur. Ent., Tech. Ser. 12, part 2, 1906. 

Isaac, P. V. Papers on Indian Tabanidae. I-VIII. Mem. Dept. Agr. Ind., Ent. 

Ser., 8: 53-62, 1924; 8: 93-109, 1925; 9: 21-28, 1925. 
Jones, T. H., and Bradley, W. G. Observations of Tabanidae (horse-flies) in 

Louisiana. Jl. Econ. Ent., 16: 307-312, 1923; 17: 45-50, 1924. 
Kelser, R. A. Transmission of surra among animals of the equine species. Philip. 

Jl. Sci., 34: 115-141, 1927. 
King, H. H. Some observations on the bionomics of Tabantis par and Tabanus 

taeniola. Bull. Ent. Res., i: 99-104, 1910. 

- . Some observations on the bionomics of Tabanus ditacniatus Macquart. 
Ibid., i: 265-274, 1911; 5: 247-258, 1914. 

- . Tabanidae. In W. Byam and R. G. Archibald, The practice of medicine 
in the tropics, i: 410-419, 1921. 

Kleine, F. K. Die Uebertragung von Filarien (lurch Chrysops. Zeit. Hyg. Infekt., 

8o: 345-349' I 9 I 5- 

Krober, O. Beitrage zur Kentniss palacrtischer Tabaniden. Arch. Naturgesch., 
Abt. A, 88: 114-164, 1922; 89: 55-118, 1924. 

- . Egyptian Tabanidae. Bull. Soc. Roy. Egypt, 18 (parts 1-3): 77-137, 1925. 

- . Die Chrysops-arten Nordamerikas einscl. Mexicos. Stett. Ent. Zeit., 87: 



* - . Die Chrysops-arten Afrikas. Zool Jahrb., Abt. Syst., Oekol. Geog. Tiere, 

53: 175-268, 1927. 

- . Catalog of the Tabanidae of South and Central America, including Mexico 
and the Antilles (trans, title). Rev. Ent., 4: 222-276, 291-333, 1934. 

Leiper, R. T. Metamorphosis of Filaria loa. Brit. Med. Jl., pp. 39-40, Jan. 4, 

1912. 
Logothetis, C., and Schwardt, H. II. Biological studies on the horse flies of New 

York. Jl. Econ. Ent., 41: 335-336, 1948. 
Lutz, Ad. Tabaniden Brasiliens und einiger Nachbarstaaten. Mem. do Instit. 

Oswaldo Cruz, 5: 142-191, 1913; 7: 51-119, 1915. 
McAtee, W. L. Facts in the life-history of Goniops chrysocoma. Proc. Ent. Soc. 

Wash., 13: 21-29, 1911. 
*MacCreary, D. Report on the Tabanidae of Delaware. Univ. Del., Agr. Exp. 

Sta., Bull. 226, 1940. 
*Marchand, W. The early stages of Tabanidae (horse-flics). Rockefeller Inst. 

Med. Res., Monograph 13, 1920. 



THE TABANIDAE AND RHAGIONIDAE 439 

Mitzmain, M. B. The biology of Tabanus striatus Fabr., the horse-fly of the 

Philippines. Philip. }1. Sci., 8: 197-218, 1913. 
. The mechanical transmission of surra by Tabanus striatus Fabr. Ibid., pp. 

223-229, 1913. 
. Collected studies on the insect transmission of Trypanosoma evansi, and a 

summary of experiments in the transmission of anthrax by biting flies. U.S. 

Pub. Hlth. Serv., Hyg. Lab., Bull. 94, 1914. 
Philip, C. B. Methods of collecting and rearing the immature stages of Tabanidae 

(Diptera). Jl. Parasit., 14: 243-253, 1928. 
* . The Tabanidae of Minnesota. Minn. Agr. Exp. Sta., Tech. Bull. 80, 

W- 
. A catalog of the blood-sucking fly family Tabanidae of the Nearctic region 

north of Mexico. Amer. Mid. Natural, 37: 257-324, 1947. 
*Schwardt, H. H. Horseflies of Arkansas. Univ. Arkansas, Agr. Exp. Sta., Bull. 

33 2 > I 93 6 - 
Stammer, H. J. Die Larvcn der Tabanidcn. Zeit. Wiss. Biol., Abt. A., Zcit. 

Morph. Okol. Ticre, i: 121-170, 1924. 
Stekhoven, J. H. S. The blood-sucking arthropods of the Dutch East Indian 

Archipelago. VI f. The Tabanidae of the Dutch East Indian Archipelago. 

Treubia, 6 (Suppl.), 1926. 
*Stone, Alan. The bionomics of some Tabanidae (Diplera). Ann. Ent. Soc. 

Arner., 23: 261-304, 1930. 
* . The horseflies of the subfamily Tabaninae of the Nearctic region. U.S. 

Dept. Agr., Misc. Pub. 305, 1938. 
Surcouf, J. M. R. Diptera. Family Tabanidae. Genera Insectorum, Fasc. 175, 

1921. 
Webb, J. L., and Wells, R. W. Horse-flies; Biologies and relation to western 

agriculture. U.S. Dept. Agr., Bull. 1218, 1924. 

RHAGIONIDAE 

Aldrich, J. M. The dipterous genus Symphoromyia in North America. Proc. 

U.S. Nat. Mus., 49: 113-142, 1915. 
Ross, H. H. The Rocky Mountain "black-fly," Symphoromyia atripes. Ann. 

Ent. Soc. Amer., 33: 254-257, 1940. 



CHAPTER XV 



The Bloodsucking 

Muscoidean Flies: Muscidae, 

Subfamily Stomoxyidinae 



THOUGH the great majority of flies belonging to the family Muscidae are 
nonbloodsucking in habit (see Chapter xvi), a small, closely related 
group, the Stomoxyidinae, are bloodsucking and are of great importance to 
the medical man and the veterinarian. These flies belong to the genera 
Stomoxys, Haematobia (Siphona), Glossina, Stygeromyia, Haematobosca, 
Bdellolarynx, and possibly a few others. The species of Stomoxys and Haema- 
tobia are widely distributed throughout the world; those of Glossina are 
restricted practically to the African continent; the other genera have repre- 
sentatives in the Oriental and Ethiopian regions. In the Americas we have 
practically only two species, Stomoxys calcitrans and Haematobia irritans, 
which are widely distributed and of considerable importance. None of these 
bloodsucking species except Glossina spp. and Stomxys spp. have, as yet, been 
incriminated as intermediate hosts of pathogenic organisms. 

THE BITING STABLE FLY 
Stomoxys calcitrans Linn. 

The biting stable fly is a close relative of the housefly but can be distin- 
guished by the sharp, piercing, nonretractile proboscis, the distinct rounded 
spots on the abdomen (Fig. 163), and the wing venation. This bloodsucking 
fly is widely distributed throughout the world and may be found wherever 
man and his domestic animals occur. It has been called the stable fly because 
of its common occurrence in and around stables, though it also frequents 
houses (particularly in late summer and autumn) and is often known as the 
"biting housefly" or "dogfly." It is a lover of the open and often occurs in 



BLOODSUCKING MUSCOIDEAN FLIES 441 

immense swarms about cattle, especially throughout our central states from 
Texas to Canada and in the Argentine Republic. This fly is a vicious biter 
and attacks a great variety of animals as well as man. Bishopp (1931) reports 
that mules, horses, cattle, hogs, dogs, cats, sheep, and goats are subject to 
attack in about the order named. The loss of blood due to these flies when 
they are abundant is a serious drain, and in severe outbreaks many animals 
may die or be so weakened that other diseases develop and cause death. Further- 
more, both Bishopp and Freeborn have recorded a marked reduction of milk 
flow and beef production when these flies are plentiful. 

The bloodsucking habit of this species caused it early to be suspected and 
later incriminated as a mechanical distributor of numerous animal and human 




Fig. 163. Biting flies. Left: Stomoxys calcitrans. Center: Glossina palpalis. Rig/it: 
Ghssina fly in resting position. 

diseases. It has been shown to be the intermediate host of at least one nematode, 
Habronema microstoma, and a cestode, Hymenolepis carioca. 

The mouth parts (Figs. 164,168) are admirably adapted for piercing and 
taking blood. Unlike the mosquito, the stable fly uses the entire proboscis in 
making the wound and both males and females suck blood. The parts consist 
of those found in the housefly (see pp. 134-139), but greatly modified to meet 
the needs of piercing. The rostrum (Fig. 164 a) is much smaller and the 
pharyngeal skeleton or fulcrum is not so well developed or heavily sclerotized. 
Owing to the acute flexure of the proboscis between the rostrum and the 
haustellum, there is a marked difference in the structure of the buccal cavity. 
The prepharynx appears as a large cylindrical duct, and the outer wall is com- 
posed of thick rings forming a supporting framework for the food channel. 
Haustellum: The labium is strongly sclerotized, enlarged, and bulbous at the 



442 MEDICAL ENTOMOLOGY 

base tapering to the apex; it appears like a club. Its upper surface is grooved 
to form a deep labial gutter in which lie the labrum and hypopharynx. Both 
of these are shorter than the haustellum and do not reach the base of the 
labella, attaining only the labellar sclerites (f urea) . The food channel is formed 




Fig. 164. Mouth parts of the stable fly (Stomoxys calcitrant), (a) Side view of the 
proboscis, (b) The labella of the proboscis with the prestomal teeth exposed, (c) Cross 
section of the labrum and hypopharynx near the middle of the proboscis. B, swollen base 
of the labium; F, fulcrum; Fc, food channel; H, haustellum; Hphy, hypopharynx; La, 
labellum; Lb, labium; Lg, labial gutter; Lm, labrum; MxPlp, maxillary palpus; P, 
pharynx; PP, prepharynx; Pt, prestomal teeth; R, rostrum; Sd, salivary duct; Sg, salivary 
duct in hypopharynx; St, stipes; W, chitinous membrane. 

by the juncture of the margins oi the labrum and the hypopharynx and opens 
directly into the pharynx (Fig. 164). Labella: The labella are small, oval lobes, 
much reduced as compared with those of the housefly (Fig. 164 b) . When at 
rest the lobes are closely appressed along their inner face, concealing com- 
pletely the cutting and tearing apparatus. When the lobes are expanded two 



BLOODSUCKING MUSCOIDEAN FLIES 443 

series of teeth are exposed, five on each side attached to the discal sclerite. Be- 
tween the teeth may be observed a number o leaflike blades that aid in the 
tearing of tissues. The labellar sclerite is not so prominent as that of the house- 
fly. In biting, the stable fly brings the rostrum and haustellum into line, the 
labella are everted, and by means of the labellar teeth and leaflike structures 
the skin is punctured. The labella are sunk into the wound so that the blood 
may be drawn up the food channel into the pharynx. 

LIFE HISTORY 

The most common breeding grounds are horse manure and straw stacks. It 
has been found breeding in cow, sheep, and other manures when mixed with 
considerable amounts of straw. Other common breeding grounds are the left- 




Fig. 165 (left). Eggs of Sfomoxys calcitrans attached to straw. (After Bishopp.) 
Fig. 166 (right). Stomoxys calcitrans. Female engorged with blood. (After 
Bishopp.) 

over grains and straw about dairies, piggeries, etc. It has also been found 
breeding in fermenting piles of grass, weeds, peanut wastes, and other vege- 
table rubbish. Intensive breeding is reported in fermenting seaweed piled up by 
the sea along the northern shores of parts of the Gulf of Mexico. Moisture is 
essential for the development of the larva. Wet, soggy manures, edges of rotting 
straw stacks, and fermenting grass piles are frequently found swarming with 
the larvae during warm, damp weather. This species has never been found 
breeding in human excrement. 

The newly emerged female requires a number of blood meals (Bishopp 
thinks at least three) for the production of eggs. She lays her eggs in irregular 
masses, usually a few to as many as 25 in a single group (Fig. 165). A female 
may lay several batches (as many as 122 eggs) before seeking another blood 
meal. A single fly may lay eggs at least three times, taking several blood meals 
between ovipositions. Bishopp (1931) records a maximum production of 632 
eggs by a single female. 



444 MEDICAL ENTOMOLOGY 

The egg is elongate-ovoid, of a creamy- white color, and measures about i mm. 
in length. The incubation period varies from two to five days, usually three 
days (at a temperature of 70 F.). The young larvae immediately bury them- 
selves in their food and development is quite rapid. With an abundance of 
food, moisture, and summer temperatures (75 to 85 F.) the larvae reach 
maturity in about two to three weeks; at higher temperatures maturity may 
be reached in n days but, in cool weather, larval development may require a 
month or more. The full-grown larva measures about 20 mm. in length, is 
white to creamy white in color, and resembles very closely the larva of the 
housefly. It may be distinguished, however, by the narrower, more pointed 
anterior end and by the posterior spiracles (Fig. 195 5). In the biting stable 
fly the posterior spiracles are widely separated, rather triangular in shape, and 
heavily sclerotized; in the housefly they are close together and nearly D-shaped. 

Pupation takes place usually in the drier parts of the breeding grounds, 
either toward the margins or near the underlying soil. The chestnut-colored 
puparia measure from 5 to 7 mm. in length and may be distinguished by the 
posterior spiracles (the spiracles are those of the last larval instar, Fig. 195). 
The pupal period varies greatly and is dependent largely on temperature, 
varying from 6 to 20 or more days. The entire life cycle from the egg to adult 
may be completed in as few as 14 days, though the normal period is usually 
three to four weeks. Under unfavorable conditions the life cycle may be greatly 
prolonged seven or more weeks. 

HABITS OF THE ADULT 

These flies are lovers of the open and commonly congregate on sunny walls, 
fences, and other exposed situations. During storms, dark days, and at nightfall 
they seek shelter, invading barns, houses, or any available shelter. On the open 
prairies they often occur in immense swarms and render life almost unendura- 
ble not only for cattle but also for man. However, their most common habitat 
is about stables and farmyards where a constant blood supply is available. 
Both the males and females are vicious bloodsuckers. The bite is painful, but 
once the beak is inserted and the flow of blood starts, little, if any, pain is 
felt. The fly requires from two to five minutes to obtain a full blood meal. 
When fully gorged (Fig. 166) it flies away rather sluggishly, settling on some 
nearby object to digest its meal. During warm weather digestion is very rapid 
and the flies require two meals a day. In cool weather they usually require a 
full day to digest a single blood meal. 

They are vigorous fliers and will follow their food supply for considerable 
distances. How far they can travel docs not seem to be known. However, 



BLOODSUCKING MUSCOIDEAN FLIES 445 

considerable distances may be traversed along roadways, the flies taking a 
blood meal, settling down to digest it, and then following another passing 
host. In this way the adults may be found long distances from their breeding 
grounds. They have been observed in trains, automobiles, etc. The life of the 
adult is rather long, varying from a few days to as many as 72 days for the 
female and 94 for the male (Mitzmain). As a rule the probable length of 
adult life is not over three or four weeks. 

In warm climates, breeding is continuous throughout the year. In the south- 
ern United States breeding is intermittent during the winter months and the 
larval life is greatly prolonged. In the colder parts of North America the winter 
months are passed normally in the larval and pupal stages. 

RELATION TO DISEASE 

Though the biting stable fly has been accused and, in some cases, apparently 
incriminated as a vector of pathogenic organisms, most of the recent work 
indicates that this fly plays but a small part in the spread of diseases. 

POLIOMYELITIS: A very considerable amount of work has been done 
on the part it may play in the transmission of poliomyelitis; though at first 
incriminated all later researches tend to prove that it has no part in the spread 
of the disease. Furthermore, the advances made in the study of the disease 
point to the improbability that any bloodsucking insect could act as a vector. 
It would seem more probable that flies that prefer fecal wastes and nasal 
discharges would be incriminated as vectors. As a matter of fact, recent work 
has incriminated such flies (see p. 476). 

TRYPANOSOMIASIS: This fly has been shown to act as a mechanical 
vector of a number of species of trypanosomes. Trypanosoma evansi, the causa- 
tive agent of surra (see Chapter xiv) of horses and mules, is known to be 
distributed by it. This is especially true when flies are abundant and blood 
meals are interrupted, the fly passing directly from one animal to another. The 
trypanosomes are transported on the proboscis and can withstand at least ten 
minutes' exposure to the air. In some parts of the world species of Stomoxys 
are regarded as important agents in the spread of surra. 

Under experimental conditions Stomoxys calcitrans has been shown capable 
of infecting susceptible animals with the following species of trypanosomes 
(there is no development or multiplication of the trypanosomes in the fly) : 

Trypanosoma brucei (causative agent of nagana) 

Trypanosoma rhodesiense (causative agent of Rhodesian sleeping sickness) 



446 MEDICAL ENTOMOLOGY 

Trypanosoma gambiense (causative agent of Gambian sleeping sickness) 
Trypanosoma cazalboui, T. dimorphon, and some others 
In order to bring about the transfer by the fly it must obtain the trypanosomes 
from an infected animal and then feed, usually within ten minutes, on a 
susceptible animal. Infection takes place through the living trypanosomes in 
or on the proboscis of the fly. 

INFECTIOUS ANEMIA OF HORSES: A virus disease of horses, in- 
fectious anemia, is widespread in North America, Europe, and Japan, and 
probably other countries. In recent years this disease has been shown to be 
transmitted by the interrupted feedings of Stomoxys calcitrant from the sick 
to the well by Scott (1922) and by Stein et al. (1942). The latter authors have 
also demonstrated sufficient virus in the mouth parts of certain tabanids as 
well as Stomoxys calcitrant that have fed on sick animals to infect susceptible 
animals. 

The genus Stomoxys contains a considerable number of species, probably 
twenty or more depending on the authority consulted. Zumpt (1938) lists some 
27 species, all of which except the one described above occur in the African 
or Oriental regions. None of these appear to be of much medical importance. 

CONTROL 

The control of the biting stable fly consists essentially in the elimination or 
reduction of their breeding grounds. The treatment and handling of manure 
for the prevention of the breeding of the housefly (see Chapter xvi) is also effec- 
tive against this species. Cleanliness in the handling of feeds in and around pig- 
geries, stables, etc., will eliminate many breeding places. However, the most 
important breeding ground of this fly is in strawstacks, especially when they 
become wet and rotting and heating take place. In order to reduce breeding, 
strawstacks should be built with vertical sides and the top so arranged as to 
shed as much water as possible. The base of the stack should be cleaned up 
so that no rotting and heating straw accumulates. All straw not intended for 
the feeding of animals or other use should be spread over the fields and 
ploughed under or it should be piled and burned. Old strawstacks should 
not be allowed to stand, for they usually become centers for the breeding of 
enormous numbers of flies. Such stacks should be distributed over the land or 
burned. Intensive breeding also occurs in fermenting vegetable rubbish, such 
as stacked peanut wastes, fermenting seaweed piled along shore lines, and any 
fermenting plant wastes. The employment of DDT sprays gives excellent 
promise for the control of the adults. In using DDT follow the directions on 
the containers. 



BLOODSUCKING MUSCOIDEAN FLIES 
THE HORN FLY 



447 



The horn fly (Haematobia irritans Linn.) is rather small, only about one- 
half as large as the biting stable fly. It is primarily a pest of cattle and acquires 
its name from its habit of clustering at the base of the horns. It rarely, if ever, 
attacks man. The species breeds exclusively in fresh cow dung. Though the 
fly is a serious pest of cattle, it is not known to be of any great importance in the 
transmission of diseases. It is not of any medical importance. 




GLOSSINA PALPALIS 

GLOSSINA TACHINOIDES 

GLOSSINA SUB-MORSITANS 

GLOSSINA MORSITANS A 



Fig. 767. Distribution of the important Glossina flies in Africa. (Adapted from the 
latest map showing this distribution.) 

^THE GLOSSINA OR TSETSE FLIES 

The Glossina or tsetse flies are primarily inhabitants of tropical and sub- 
tropical Africa, various species occupying different or overlapping areas of 
the continent. The only record of any species having been found outside 
Africa is from southeast Arabia and this record is doubtful. Their distribution 
in Africa lies between a line drawn from the mouth of the Senegal River east 



448 MEDICAL ENTOMOLOGY 

through Lake Chad to the Nile and thence to the coast at about 4 North lati- 
tude south to a line drawn from the mouth of the Cunene River east through 
the southern boundary of Angola to the northeastern extremity of St. Lucia 
Lake in Zululand (Austen). Within this area Newstead (1924) recognizes 
20 species, i subspecies, and 5 varieties. The various species are not widely 
distributed throughout this vast region but occupy certain areas, some closely 
restricted to districts suitable for their development, as G. swynnertoni Austen, 
or widely distributed over a vast area, as G. palpalis and G. morsitans and 
their varieties (Fig. 167). This genus is probably one of the most important 



Ant _ 




Fig. 168. Heads of bloodsucking flies. Left: Stomoxys calcitrant. Right: Glossina sp. a, 
arista (note the difference); Ant, antenna; G, the gena; Lb, labium; MxPlp, maxillary 
palpi (within these lie die labium and piercing mouth parts) ; V, vibrissa. 

among insects. The flies are the transmitters of many species of trypanosomes, 
especially the important pathogenic species those causing sleeping sickness of 
man and nagana of cattle, horses, and a wide variety of game animals. 

In structure these flies closely resemble Stomoxys but they differ rather 
markedly in certain features. Their life histories more nearly approach some 
of those of the Pupipara rather than those of the typical muscids. The more 
important external characteristics can be summarized here but very briefly. 
The adults, when at rest, hold their wings crossed scissorlike (see Fig. 163) 
over the abdomen. The wing venation is also quite distinctive. The proboscis 
is held in front of the head and appears large and stout owing to the develop- 



BLOODSUCKING MUSCOIDEAN FLIES 449 

ment of the maxillary palpi. The palpi are thick, porrect structures. Each palpus 
has a broad, flat channel on its inner face. The proboscis lies within the channel 
formed by the apposition of the palpi (Fig. 168). 

The proboscis consists of the rostrum, haustellum, and labella. The rostrum 
is very short, pyramidal in shape, and compact. Extending at right angles 
from its distal end lies the haustellum. The haustellum resembles that of 
Stomoxys. At its base is a large, bulbous structure usually known as the "bulb." 
The labium extends to the labella as an elongated sclerotized structure and 
grooved along its upper surface (the labial gutter). Within the labial gutter 
lie the labrum and hypopharynx. The labella are not well marked off from 
the labium proper. On the inner face of the labella are rasps, prestomal teeth, 
and certain accessory structures that serve to penetrate when the fly seeks blood. 
Both males and females are bloodsucking in habit. 

BIOLOGY OF GLOSS1NA SPECIES 

Though the Glossina flies are distributed over an extensive area in Africa, 
they are not found everywhere but are restricted to particular tracts, known as 
"fly belts." These "belts" may be very limited owing to the conditions neces- 
sary for the species to obtain food, shelter, and an opportunity to reproduce. As 
the knowledge of these flies is far from complete, the biology of the two most 
important species is here briefly considered. 

GLOSSINA PALPALIS ROBINEAU-DES VOIDY : This species (Fig. 
163), the transmitter of Gambian sleeping sickness of man, is distributed 
throughout central Africa (Fig. 167), in an area bounded by a line drawn from 
the mouth of the Senegal River east to southern Ethiopia, thence south to the 
southern end of Lake Tanganyika, and west to central Angola (here reaching 
the Atlantic Ocean). Within this extensive area the fly occurs primarily along 
watercourses, rivers, and lakes bordered with forests having undergrowths. 
The flies do not wander far from water, generally not over a few hundred 
yards. Shade is essential, but it may vary from dense vegetation to more or 
less open forest or even the tall grass and sedges along rivers or lakes. The flies 
are most active during the hours of sunshine and are attracted to moving 
objects. They seem to prefer dark skins and clothes to light-colored skins or 
clothes. The preferred food of this species seems to be the blood of man, 
though they attack various domestic and game animals such as pigs, goats, 
monkeys, hippopotamuses, crocodiles, bushbucks, waterbucks, mongeese, etc. 
The adults are long lived, the average length of life varying from about 100 to 
over 250 days. 



450 MEDICAL ENTOMOLOGY 

LIFE HISTORY: Unlike most of the muscoidean flies, the Glossina species do 
not lay eggs. Though the eggs are formed they pass singly into a uterine pouch 
where they hatch. Only a single egg is received by the uterine pouch at a time. 
Here the egg hatches and the larva completes its growth within this peculiar 
uterus, The food for growth is supplied by special glands, the so-called "milk 
glands." Roubaud found that the period of gestation of the first larva produced 
by a female was 22 days and the intervals between subsequent larvae varied 
from 9 to 10 days. The mature larvae are deposited in dry soil situated in close 
proximity to water and in the shade. The pupal period varies from 25 to 55 days. 

GLOSSINA MORSITANS WESTWOOD AND G. SUB-MORSI- 
TANS: These species occupy extensive areas in central, western, and eastern 
Africa (Fig. 167). The "fly belts" of these species are not so restricted as of 
G. palpalis. They have a widespread distribution during the wet season. Shade 
and moisture do not appear so essential, for these flies may be found long 
distances from water. During the dry season they concentrate in certain areas 
where there is some shade, as among the nondcciduous trees or fresh green 
grass in the extensive, open, low-lying country. This green grass is supported 
by subsoil water and affords excellent grazing for game animals, which, in 
turn, furnish an abundant food supply for the flies. The flies travel considera- 
ble distances, especially when following animals. There seems no doubt that 
they can migrate from five to ten miles. Many observers state that the flies 
are most active during the cool of the day, morning and evening hours, 
though others record them as biting in the brightest sunshine in the heat 
of the day. 

LIFE HISTORY (G. morsituns] : Unlike G. palpalis, G. morsitans is not de- 
pendent on the proximity of water for its breeding grounds. The females 
deposit mature larvae in loose, dry soil; the pupae have also been found in 
hard soil, in wood ash from forest fires, and in other situations. Some kind of 
shade seems essential though this may be furnished by shrubbery, fallen trees, 
overhanging rocks, tree hollows, or burrows in the ground. In general the 
breeding grounds of this species appear to be widely scattered over its entire 
range. The pupal period varies from about 21 to 60 or more days, dependent 
largely on temperature. 

RELATION TO DISEASE 

The Glossina flies are the transmitters of various species of trypanosomes, 
the most important affecting man being Trypanosoma gambiense (the causa- 
tive agent of Gambian sleeping sickness), T. rhodesiense (causative agent of 



BLOODSUCKING MUSCOIDEAN FLIES 451 

Rhodesian sleeping sickness and believed to be a variety of the following spe- 
cies), and T. brucei (causative agent of nagana or tsetse-fly disease of horses, 
dogs, cattle, and game animals). Trypanosomiasis is the general term applied to 
infection with any species of Trypanosoma. Trypanosoma species are Protozoa, 
belonging to the class Mastigophora, subclass Zoomastigina, family Trypano- 
somatidae. The trypanosomes are found as parasites in the blood stream, occa- 
sionally in the tissues, of vertebrates. A great number of species has been 
described, and many of them, if not all (with the exception of T. equiperdum 
and T. evans'i) require an invertebrate host for the completion of their life 
cycle and transmission to new hosts. The body of a typical trypanosome (Fig. 




Fig. 169. Trypanosoma rhodesiense in blood of guinea pig. 

169) appears as a curved, narrow leaf or flattened blade. The ends are tapering, 
one end usually being blunter than the other. The nucleus is generally central 
and the blepharoblast lies near the blunt or posterior end. From the kineto- 
nucleus arises the flagellum, which passes out of the body and forms the outer 
border of the undulating membrane and may be continued as a free flagellum 
beyond the body. Reproduction is by binary fission. 

Though there are numerous species of trypanosomes, only a comparatively 
few are known to be pathogenic. The species known to be pathogenic to man 
are T. gambiense, T. rhodesiense (Fig. 169), and T. cruzi. The first two are 
restricted to tropical Africa and are transmitted by Glossina flies; the last one 
occurs in South America and is transmitted by bugs of the family Reduviidae 
(see pp. 184-187). 



452 MEDICAL ENTOMOLOGY 

Trypanosoma gambiensc has a distribution in Africa that closely approxi- 
mates that of Glossina palpalis. Sleeping sickness has been known for nearly 
two hundred years, and various accounts of its peculiar manifestations were 
written in the early part of the nineteenth century, particularly by those en- 
gaged in the slave trade. The disease was brought over to the West Indian 
Islands but never became established nor did it spread among the population 
for reasons now well known. Though restricted at first to an extensive area in 
West Africa, its distribution throughout that continent began with the com- 
mercial development in the eighties of the last century. It is believed that 
Stanley, the African explorer, brought the disease into the heart of the con- 
tinent and to the Uganda and Great Lakes region during his trip across from 
the Congo to the Nile (1887-1889). In 1901 an epidemic of the disease broke 
out in Uganda, and since that time intensive investigations have been con- 
ducted by numerous workers in various parts of Africa. 

Sleeping sickness manifests itself in two rather distinct phases an inter- 
mittent fever phase that may last for months or years and the so-called true 
"sleeping sickness." The first stage is characterized f)y irregular fever, debility, 
languor, vague pains, enlargement of the glands of the neck, edematous swell- 
ings, and generally an erythematous rash. This condition may continue for 
months or years (now called "trypanosomiasis" stage) and is practically always 
followed by the second phase, the "sleeping sickness" stage (due to the invasion 
of the nervous system). The drowsiness and languor become pronounced, no 
interest is taken in the surroundings, and no attempt is made to obtain food 
though the patient will eat if food is offered. The fever continues, wasting 
becomes pronounced, and the patient passes into a state of coma till death 
intervenes (Fig. 170). 

Although the disease was long known, it was not till Forde observed an 
organism (which he thought at first was a filaria) in the blood of a European 
patient in Gambia suffering from a peculiar fever known as "Gambian 
fever" that led to the discovery of the causative agent. Button (1902) saw 
Forde's preparations and pronounced the organism a Trypanosoma, which he 
later described as Trypanosoma gambiense. Castellani (1903), working in 
Uganda, discovered a trypanosome in the cerebrospinal fluid of natives suffer- 
ing from sleeping sickness, described it as T. ugandense, and asserted it to be 
the etiological agent of the disease. Bruce and Nabarro (1903) confirmed 
Castellani's work and also recovered the parasite from the blood in the early 
and later stages of the disease. It was soon determined that T. ugandense 
was identical with T. gambiense, so that the etiological agents of West Coast 
and central African sleeping sickness are the same. Since then numerous 



BLOODSUCKING MUSCOIDEAN FLIES 453 

investigators have fully confirmed and extended these results. Bruce and 
Nabarro (1903), by means of a study of the distribution of the disease and the 
species of tsetse fly (Glossina palpalis) present in the area, concluded that this 
fly was the agent responsible for its spread. This they confirmed by feeding ex- 
periments, transmitting trypanosomes by the fly from patients to healthy 
monkeys and also infecting monkeys by flies caught in the wild. 

Though Glossina flies had now been shown to transmit (in practically all 
experiments probably mechanically though some workers thought there must 
be a cyclical development in the fly) two species of trypanosomes (T. brucei 
by G. morsitans and T. gambiense by G. palpalis), it was not known what 




Fig. 170. Sleeping sickness. A group of natives in differ- 
ent stages of the disease. (From Byan and Archibald, The 
Practice of Medicine in the Tropics.) 

relation these parasites bore to the flies. Kleine (1909) demonstrated that the 
trypanosomes undergo a cyclical development in the flies and that once a fly 
is infected it may remain infected for a considerable period. These results have 
been fully confirmed, adding another link in the etiological chain of this 
disease. Finally Bruce and his co-workers (1910, 1911) showed the possibility 
of domestic cattle and wild game acting as reservoirs of T. gambiense. Since 
then, owing to the extreme difficulty of identifying the different species of 
trypanosomes, many confusing reports on this phase of the parasite's host have 
been published. It would seem, according to Wenyon (1926), that "occa- 
sionally domestic animals Jiving in association with human beings amongst 
whom this disease occurs may acquire the infection, but there is little or no 
evidence to incriminate the wild game as reservoirs of this trypanosome." 



454 MEDICAL ENTOMOLOGY 

The cyclical development of T. gambiense in Glossina pulpalis has been most 
carefully investigated by Robertson (1913). When the fly ingests blood con- 
taining trypanosomes, one of several alternatives may occur: 

1. All the trypanosomes may be digested in 50 to 72 hours and disappear 
from the gut. 

2. Some of the trypanosomes may persist in the crop and gut but disappear 
with the next feeding. 

3. They may survive in the gut and multiply in the first blood meal even 
though a second feeding has taken place. These may be swept out when the 
original meal is digested. 

4. Some may persist and develop in the crop with successive feedings, but 
no infection will occur as there is never a permanent crop infection. 

5. Some will persist in the gut after the first meal has been entirely replaced 
by the second blood meal. 

This last condition brings about a permanent infection of the fly. The 
trypanosomes multiply rapidly and from the tenth to the fifteenth day distinct, 
slenderer forms arise and almost completely fill the posterior part of the mid- 
gut. These push forward to the proventriculus, thence up into the hypo- 
pharynx and along the salivary ducts into the salivary glands. Arriving in 
the salivary glands they gradually change to broad crithiclial forms, multiply, 
and fill up the glandular cavity. Here soon appear stumpy forms, closely 
resembling the blood type, and these arc the infective forms. The entire 
cyclical development, from the time of the ingestion of blood trypanosomes 
to the appearance of the infective salivary forms, requires from 20 to ^o days. 
During this period the fly must have access to blood meals when needed. 
Once a fly becomes infected it remains so for probably the rest of its life. 

In addition to G. palpalis the following species have been shown, experi- 
mentally, to be capable of transmitting T. gambiense: G. morsituns, G. palli- 
dipes, G. jusca, and G. tachinoides. 

Rhodcsian sleeping sickness is caUsSed by T. rhodesiense (Fig. 169) which 
was recognized and described by Stephens and Fantham in 1910. The disease 
runs a more rapid course and brings about death in a few months (three or 
four), death usually intervening before the "sleeping stage" develops. The 
parasite is more pathogenic to laboratory animals, monkeys dying in from 
8 to 14 days after infection, whereas with T. gambiense death may occur in from 
27 to 159 days; in rats, T. rhodcsiense is extremely virulent, whereas T. gam- 
biense produces a chronic infection. Many investigators believe that T. rho- 
desiense is but a strain of T. brucei which has become capable of infecting man. 

This type of sleeping sickness is rather restricted in its distribution, occurring 



BLOODSUCKING MUSCOIDEAN FLIES 455 

in parts of Rhodesia, about Lake Nyasa, in the northeast part of Mozambique, 
and in. the southeastern corner of Tanganyika. This disease was shown by 
Kinghorn and Yorkc (1912) to be distributed by G. morsitans and confirmed 
by Bruce and his co-workers (1914). The latter also incriminated G. brevipalpis. 
The developmental cycle of the parasite in the fly is similar to that of T. gam- 
biensc in G. palpalis. 

Nagana or tsetse-fly disease of cattle is caused by T. bntcci. This parasite 
was discovered by Bruce in 1895, who also showed (1897) that it was trans- 
mitted by Glossina morsitans. The disease is widespread in Africa, extending 
from Zululand to the Sudan. T. brucei is probably the most virulent of all 
known pathogenic trypanosomes. It is inoculable into practically all mammals. 
Horses, mules, donkeys, and camels usually die within a fortnight to tbrce 
weeks; cattle are not killed so rapidly but very few recover; pigs succumb 
quickly and dogs die in about two weeks after inoculation; rats and mice are 
very susceptible, while cats are more tolerant; monkeys, with the exception 
of baboons, die usually in three or four weeks; many other domestic animals 
are susceptible, and the disease runs a rather rapid course (Wenyon). Bruce 
(1^95) found what he considered this species in many kinds of wild game 
and later demonstrated that in Nyasaland nearly 32 per cent of the wild game 
harbored T. brucei or other species pathogenic to domestic animals. This work 
has been confirmed by other workers and the reservoir of this trypanosome 
definitely established. 

Though this trypanosome is primarily a parasite of numerous species of 
mammals, man has long been considered immune. Since the discovery of T. 
rhodesiense by Stephens and Fantham, many investigators consider this human 
species as but a strain of T. brucei that has become adapted to man (Wenyon, 
1926). Kleine (192$) maintains that T. rhodesicnse is a distinct species and that 
its animal reservoir has not yet been ascertained. 

The species of Glossina flies that are known to transmit T. brucei are G. 
morsitans, G. brevipalpis, G. pallidipes, G. palpalis, and G. tachinoides. 

CONTROL OF GLOSSINA FLIES 

As no very effective treatment for sleeping sickness of man (except the 
use of certain drugs, and these do not prevent reinfection or guarantee a cure), 
nagana of horses, mules, cattle, etc., and other trypanosomiascs has yet been 
devised, the problem of the control of Glossina flies is a major one in many 
parts of Africa. Sleeping sickness has devastated many populous districts 
(Uganda) of Africa, rendered much agricultural land unfit for habitation, 
and threatens the future development of some of the most fertile regions of the 



456 MEDICAL ENTOMOLOGY 

world. Though extensive investigations have been and are now being carried 
on, the problem of tsetse-fly control is a baffling one. At the present time much 
progress has been made in the reduction of Glossina flies by some or all of 
the following methods: (i) by clearing the jungle along the "fly belts," by 
using the same methods about native villages, and by removing forested areas 
along water courses (it is only necessary to clear some 50 to 100 yards in these 
areas as the flies rarely move very far from protected growths) ; (2) by trapping 
the flies in those areas where they are numerous, especially near populated 
districts; (3) by avoiding "fly belts" so as not to introduce the disease into 
free areas; (4) by wearing white clothing (the flies prefer dark surfaces on 
which to alight) and by wearing head nets, gloves, and protective clothing; 
no satisfactory repellent has yet been developed; (5) by constructing better 
housing, using screens, and improving sanitation; and (6) by destroying game 
animals. The latter method, though practiced in some districts, does not seem 
worth while as domestic animals may also serve as reservoirs. However their 
reduction in populous areas may serve a useful purpose. More recently the use 
of various DDT formulations in certain areas shows promise. 

REFERENCES 

*Austen, E. E., and Hegh, E. Tsetse-flies. London, 1922. 

Bcquacrt, }. Tsetse-flies past and present (Diptera, Muscoidea). Em. News, 

41: 158-164, 202-203, 22 7~ 2 33> I 93- 

Bishopp, F. C. The stable-fly; how to prevent its annoyance and its losses to live- 
stock. U.S. Dept. Agr., Farmers' Bull. 1097, 1931. 
Bruce, D. Preliminary report on the tsetse-fly disease or nagana in Zululand. 

Umbobo, 1895. 
. Further report on the tsetse-fly disease or nagana in Zululand. London, 

1897. 
, and Nabarro, D. Progress report on sleeping sickness in Uganda. Repts. 

Sleep. Sick. Comm., Roy. Soc., No. i, 1903. 
Buxton, P. A. Studies on Soils in Relation to the Biology of Glossina submorsitans 

and tachinoides in the north of Nigeria. With An Appendix by K. Mellanby. 

Bull. Ent. Res., 27: 281-287, 1936. 
, and Lewis, D. J. Climate and tsetse-flies; laboratory studies upon Glossina 

submorsitans and tachinoides. Phil. Trans. Roy. Soc., B 224: 175-240, 1934. 
Carpenter, G. D. H. A naturalist on Lake Victoria, with an account of sleeping 

sickness and the tsetse-fly. London, 1920. 

Castellani, A. Trypanosoma in sleeping sickness. Brit. Med. Jl., i: 1218, 1903. 
Dicke, B. H. The tsetse-fly's influence on South African history. S. Afr. Jl. Sci., 

29: 792-796, 1932. 



BLOODSUCKING MUSCOIDEAN FLIES 457 

Duke, H. L. Some observations on the bionomics of Clossina palpalis on the 

islands of Victoria Nyanza. Bull. Ent. Res., 9: 263-270, 1919. 
Dutton, }. E. Trypanosoma in man. Brit. Med. Jl., Jan. 4, p. 42; Sept. 20, p. 88 1, 

1902. 
*Enderlein, G. Ucber die ^Classification der Stomoxinae (blutsaugende Musciden) 

und neue Arten aus Europa und Afrika. Zcit. Angew. Ent., 14: 356-368, 1928. 
*Fiske, W. W. Investigations into the bionomics of Glossina palpalis. Bull. Ent. 

Res., 10: 347-463, 1920. 
Forde, R. M. Some clinical notes on a European patient in whose blood a try- 

panosome was observed. JL Trop. Med. and Hyg., 5: 261-263, 1902. 
Griinberg, Karl. Die blutsaugenden Dipteren. Jena, 1907. 
Harris, R. H. T. P. Some facts and figures regarding the attempted control 

of Glossina pallidipcs in Zululand. S. Afr. Jl. Sci., 29: 495-507, 1932. 
*Hegh, Emile. Les tse-tses. Brussels, 1929. 
*Hindle, E. Plies in relation to disease. Blood-sucking flies. Cambridge Pub. 

Health Series, Cambridge, Eng., 1914. 
Jackson, C. H. N. Some new methods in the study of Glossina morsitans. Proc. 

Zool. Soc. Lond., Part 4: 811-896, 1936. 
Jobling, B. A revision of the structure of the head, mouth-parts and salivary 

glands of Glossina palpalis Rob.-Desv. Parasitology, 24: 449-490, 1933. 
*Kinghorn, A., and Yorke, W. On the transmission of human trypanosomes by 

Glossina morsitans Westw.; and on the occurrence of human trypanosomes in 

game. Ann. Trop. Med. Parasit., 6: 1-23, 269-285, 1912. 

Kleine, F. K. Positive Infektionsversuche mit Trypanosoma bruccl durch Glos- 
sina palpalis. Deutsch. Med. Woch. 35: 469, 1909. 
. Zur Flpidemiologie der Schlafkrankheit. Deutsch. Med. Woch., 49: 505- 

506, 1923. 
Mcllanby, Helen. Experimental work on reproduction in the tsetse-fly, Glossina 

palpalis. Parasitology, 29: 131-141, 1937. 
Melvin, R. Notes on the biology of the stable-fly, Stomoxys calcitrant. Ann. Ent. 

Soc. Amer., 24: 436-438, 1938. 
Mitzmain, M. B. The role of Stomoxys calcitrans in the transmission of Trypano- 

soma evansi. Philip. Jl. Sci., B, 7: 475-518, 1912. 
. The bionomics of Stomoxys calcitrans Linnaeus; a preliminary account. 

Ibid., 8: 29-48, 1913. 
. Collected studies on the insect transmission of Trypanosoma evansi, and 

summary of experiments in the transmission of anthrax by biting flies. U.S. Pub. 

Health Serv,, Hyg. Lab., Bull. 94, 1914. 
Moggridge, J. Y. Experiments on the crossing of open spaces by Glossina swynner- 

toni. Bull. Ent. Res., 27: 435-448, 1936. 
*Nash, T. A. M. The ecology of Glossina morsitans Westw., and two possible 

methods for its destruction. Ibid., 24: 107-157, 163-195, 1933. 



458 MEDICAL ENTOMOLOGY 

Nash, T. A. M. Climate, the vital factor in the ecology of Glossina. Ibid., 28: 

75-127, 1937. 
Nettles, W. C. An unusual outbreak of stable fly and its control. Jl. Econ. Ent., 

27: 1197-1198,1934. 
Newstead, R. On the life-history of Stomoxys calcitrant Linn. Jl. Econ. Biology, 

i : 157-166, 1906. 

** , Evans, A. M., and Potts, W. H. Guide to the study of tsetse-flies. Liver- 
pool School Trop. Med., Mem., n.s., i, 1924. 
Patton, W. S. Studies on the higher Diptera. II. The genus Stomoxys GeofTroy 

(Sens. lat.). Ann. Trop. Med. Parasit., 27: 501-537, 1933. 
Robertson, M. Notes on certain aspects of the development of Trypanosoma- 

gambiense in Glossina palpalis. Proc. Roy. Soc., B, 85: 241-248, 1912. 
. Notes on the life-history of Trypanosoma gambicnsc, with a brief reference 

to the cycles of Trypanosoma nanum and Trypanosoma pecorum in Glossina 

palpalis. Phil. Trans. Roy. Soc., B, 203: 161-184, 1913. 
*Scguy, E. Etude sur les Stomoxyclincs et particulieremcnt dcs mouches Char- 

bonneuses du genre Stomoxys. Encycl. Ent., B., II Dipt., 8: 15-58, 1935. 
Simmons, S. W., and Dove, W. E. Breeding places of the stable fly or "dog fly," 

Stomoxys calcitrans (L), in northwestern Florida. J. Econ. Ent., 34: 457-462, 

1941. 
Stephens, J. W. W., and Eantham, H. B. On the peculiar morphology of a 

trypanosome from a case of sleeping sickness and the possibility of its being a 

new species (T. rhodesiensc). Ann. Trop. Med. Parasit., 4: 343-350, 1910. 
Swynncrton, C. F. M. The tsetse-flies of East Africa. A first study of their ecology, 

with a view to their control. Trans. Ent. Soc. Lond., Vol. 84, 1936. 
Symes, C. B., and Vane, R. T. The eradication of G. palpalis from river areas 

by the "block" method. Nairobi, Kenya, 1957. 
*Wilhelmi, J. Die gemeine Stechfliege (Wadcnstccher); Untenmchungen liber 

die Biologic der Stomoxys calcitrans L. Zeit. Angew. Ent., Monograph 2, 1917. 
*Zumpt, F. Die Tsetsefliegcn. Ihre Erkennungsmerkmale, Lebensweise und 

Bckarnpfung. Jena, 1936. 



CHAPTER XVI 



The Housefly and Its Allies 1 



THE housefly (Mtisca domcstica Linn.), or the "typhoid-fly" as it is desig- 
nated by some writers, is the most common and abundant fly in and about 
homes throughout the world; it is the animal most commonly associated with 
man; it is distributed from the subpolar regions to the tropics, where it occurs 
in enormous numbers. 

DESCRIPTION: The housefly (Fig. 171) is mouse-gray in general color. 
The thorax is gray, marked by four equally broad, dark, longitudinal stripes, 
most clearly defined in front. The abdomen has the sides of the basal half 
yellowish and somewhat transparent; the posterior segment is brownish black 
and a dark longitudinal line extends along the middle of the dorsum. The legs 
are blackish brown. The wings are clear though somewhat yellowish at the 
base. The venation is rather distinctive (Fig. 172); the fourth longitudinal 
vein is sharply bent upwards so as nearly to meet the vein in front. The 
squamae (calypteres) are large, opaque, yellowish. The adult measures 6 to 
7 mm. in length with a wing expanse of 13 to 15 mm. 

LIFE HISTORY: The housefly undergoes a complete metamorphosis. 
Mating takes place in from 2 to 12 days after the adults emerge. Oviposition 
may begin within 2 to 3 days after copulation. The female deposits its eggs 
singly, laying from too to 150 eggs at a time in a batch (Fig. 173). Each female 
lays several batches, four or more, during her lifetime, that is, from 400 to 600 
eggs. Dunn (1923) records remarkable fertility for the housefly in Panama, 
a single female laying 2^87 eggs during a period of 31 clays. 

The egg is white, oval in shape, and measures about i mm: in length. Along 
the dorsal surface of the egg are two distinct riblike thickenings. The eggs 
hatch in from 12 to 24 hous (at temperatures of from 68 to 80 F.), though 



1 For the identification of the families in this group of flies, consult the key on pp. 
228-231, beginning at No. 11. 



460 MEDICAL ENTOMOLOGY 

hatching may be delayed by lower, or somewhat hastened by higher, tempera- 



tures. 



The larva (Fig. 173) develops very rapidly when food supply and tempera- 
ture are favorable. There are three larval stages or instars. The last stage is 
reached in from four to eight days. The mature larva measures about 12 mm. 
in length. It is white in color and conically-cylindrical in shape. The body tapers 




Fig. 777. The housefly, Musca domestica. (Courtesy Department of Agricul- 
ture, Division of Entomology, Canada.) 

off gradually from the middle region to the anterior or head end. The posterior 
is cylindrical but the last segment is larger and obliquely truncate. The body 
is composed of twelve visible segments and is legless. Near the middle of the 
dejUyjjL^ of the last segment are the posterior spiracles MynD-shaped 
sclerotizcd rings placed rather close together (Fig. 195 4). Each spiracle con- 
sists of a ring that encloses three sinuous slits through which the air passes 
to the tracheal system. On the inner flat side of the ring is a heavy sclerotized 
area, the so-called "button." The anterior spiracles are situated laterally at the 



THE HOUSEFLY AND ITS ALLIES 461 

posterior border of the third body segment. Each spiracle consists of a fan- 
shaped body bearing six to eight small papilliform processes. 

The larva of the housefly, like all muscid larvae, lacks a true head : the first 
segment (usually termed the "pseudocephalon") is nearly all retracted within 
the body. At the anterior end of the larva is seen a heavi